LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 

Deceived 
Accessions  No.V'<w.  Class  No. 


i 


K. 


A  TEXT-BOOK 


OF 


ORDNANCE  AND  GUNNERY. 


PREPARED' FOR  THE  USE  OF  CADETS  OF  THE 
U.   S.  MILITARY  ACADEMY. 


BY 


CAPTAIN   LAWRENCE   L.   BRUFF, 

ORDNANCE  DEPARTMENT,  U.  S.  ARMY,' 
Instructor  of  Ordnance  and  Gunnery  at  the  U.  S.  Military  Academy^ 


FIRST   EDITION. 

FIRST   THOUSAND. 


Of  TBGi 

'jmiB 

NEW   YORK: 

JOHN   WILEY   &   SONS. 

LONDON:   CHAPMAN  &  HALL,   LIMITED. 

1896. 


Copyright,  1896, 

BY 
LAWRENCE  L.  BRUFF. 


ROBBRT   DRUMMOND,   ELECTROTYPER   ANP   PRINTER,    NEW   YORK. 


THE  present  text-book  has  been  compiled  with  the  object 
of  presenting  as  clearly  as  possible  the  elementary  principles 
of  the  course  in  Ordnance  and  Gunnery  as  taught  at  the 
Military  Academy,  and  of  so  arranging  it  that  it  can  be 
readily  used  for  recitations  in  the  section-room.  For  this 
purpose  it  has  been  divided  into  separate  subjects,  each  as 
well  denned  as  possible.  In  its  preparation  I  -have  followed 
the  lines  laid  down  by  my  predecessor  Capt.  Henry  Met- 
calfe,  U.  S.  A.,  retired,  from  whose  labors  in  the  same  field  I 
have  derived  the  greatest  assistance.  I  am  also  under  many 
obligations  to  those  who  have  kindly  criticised  and  cor- 
rected my  work  in  many  important  particulars,  and  especi- 
ally to  Colonel  Buffington,  Captains  Smith,  Blunt,  Birnie, 
Mitcham  and  Crozier,  Ordnance  Department,  and  to  Mr. 
W.  R.  Quinan  of  the  California  Powder  Company. 

Lieut.  Babbitt,  Ordnance  Department,  my  assistant  at 
the  Military  Academy,  has  made  many  valuable  criticisms 
and  suggestions  which  have  added  greatly  to  the  clearness 
of  the  work. 

WEST  POINT,  March  10,  1896. 

iii 


TABLE  OF  CONTENTS. 


PAGE 

CHAPTER   I. 

GUNPOWDERAND    INTERIOR  BALLISTICS* I 

CHAPTER   II. 
HIGH  EXPLOSIVES  AND  SMOKELESS  POWDERS.^ 105 

CHAPTER   III. 
GUNS 136 

CHAPTER  IV. 
PROJECTILES  AND  ARMOR 279 

CHAPTER  V. 
FUZES  and  PRIMERS 328 

CHAPTER  VI. 
EXTERIOR  BALLISTICS '. 347 

CHAPTER  VII. 
ARTILLERY  CARRIAGES  ;  THEORY  OF  RECOIL , 389 

CHAPTER  VIII. 
POINTING  ;  PROBABILITY  OF  FIRE 466 

CHAPTER  IX. 
PORTABLE  ARMS 528 

CHAPTER  X. 

MACHINE  AND  RAPID-FIRE  GUNS 589 

INDEX 639 


[IHU7BRSITT] 

TEXT-BOOK  OF  ORDNANCE  AND  GUNNERY. 


CHAPTER   I. 
GUNPOWDER  AND   INTERIOR  BALLISTICS. 

GUNPOWDER. 

1.  Composition— Manufacture. 

COMPOSITION. — Gunpowder  is  a  mechanical  mixture  of 
nitre,  charcoal,  and  sulphur,  in  the  proportions  of  75  parts 
nitre,  15  charcoal,  and  10  sulphur. 

The  nitre  furnishes  the  oxygen  to  burn  the  charcoal  ancf 
sulphur.  The  charcoal  is  the  principal  combustible  body,, 
and  the  smphur  gives  density  to  the  grain  and  lowers  its 
point  of  ignition. 

The  nitre  is  purified  by  solution  in  water  and  crystalliza- 
tion, the  sulphur  by  distillation,  and  the  charcoal  is  care- 
fully prepared  to  make  it  as  uniform  as  possible. 

The  distinguishing  characteristic  of  charcoal  is  its  color, 
being  brown  when  prepared  at  a  temperature  up  to  280° 
Cent.,  from  this  to  340°  red,  and  beyond  340°  black. 

Brown  charcoal  is  now  generally  used  for  powder. 

MANUFACTURE. — The  operations  are  : 

r.  Pulverizing,  mixing,  and  incorporating  the  ingre- 
dients. 

2.  Compressing  this  mixture  to  give  it  a  proper  density. 

3.  Dividing  the  dense  mass  into  grains. 

4.  Finishing  the  grains. 

Pulverizing  and  Mixing. — The  nitre  is  in  fine  crystals 
when  received;  the  sulphur  is  rolled  in  an  iron  barrel  with 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


FIG.  i. 


iron  balls ;   and   the   charcoal  also,    or  the  latter   may   be 
ground  in  a  mill 

The  ingredients  are  mixed  by  hand  or  by  machine. 

Incorporating. — To  make  the  mixture  thorough,  the  above 

composition  is  moistened  and  incorporated  in  a  wheel  mill. 

This  mill  consists  of   a  pair  of  heavy  cast-iron  cylindrical 

rollers  running   in  a    circular    trough   (Fig.   i).     By  their 

action  they  grind  the  products 
together,  and  give  a  thorough 
mixture. 

This  is  the  most  important 
operation  in  the  manufacture, 
and  if  not  well  done  no  subse- 
quent operation  can  remedy  it. 

Pressing. — The  mill-cake  which 
comes  from  the  "  wheel  mill  "  is 
broken  up,  moistened,  and  placed, 
in  layers  about  2  inches  thick, 
under  a  hydraulic  press.  The 

layers  are  reduced  to  a  thickness  of  about  i  inch  and  be- 
come very  dense  and  hard,  and  this  is  called  "  press-cake." 

Graining. — In  ordinary  powders,  the  press-cake  is  broken 
up  into  grains  of  various  sizes.  The  object  of  this  is  to 
increase  the  surface  of  combustion,  and  to  regulate  it 
according  to  the  gun  in  which  it  is  to  be  used.  The  grain- 
ing is  done  by  rollers  acting  on  the  press-cake,  and  the 
grains  are  afterwards  assorted  with  sieves. 

Glazing. — To  remove  the  sharp  angles,  and  give  uniform 
density  to  the  surface,  the  grains  are  placed  in  a  wooden 
barrel  revolving  on  its  axis.  They  are  thus  made  to  rub 
against  each  other,  and  accomplish,  by  their  mutual  attrition, 
the  objects  mentioned. 

Drying  and  Dusting. — The  excess  of  moisture  in  the 
powder  is  now  removed  by  a  current  of  warm,  dry  air,  and 
the  dust  which  has  been  formed  on  the  grains  is  removed 
by  passing  them  through  a  revolving  sieve. 

Blending  and  Marking. — Different  lots  of  the  same  kind 
of  powder  are  mixed,  to  overcome,  as  much  as  possible, 
irregularities  of  manufacture.  In  our  service  the  powder 


GUNPOWDER  AND    INTERIOR  BALLISTICS. 


is  packed  in  loo-lb.  barrels  and  marked  with  certain  letters, 
as  I.  K.  B.,  E.  V.  X.,  etc.,  the  first  two  letters  denoting  the 
kind  of  powder,  or  its  use,  and  the  third  letter  the  lot. 

In  foreign  services  the  letters  indicate  the  use  directly : 
as,  R.  F.  G.,  rifle  fine  grain  ;  P.,  pebble  ;  etc. 

Government  powder  is  purchased  by  contract. 

2.  Specific  Gravity  and  Gravimetric  Density. 

THE  SPECIFIC  GRAVITY,  or  actual  density,  of  gunpowder, 
like  that  of  any  solid  body,  is  the  weight  of  a  given  volume 
referred  to  that  of  an  equal  volume  of  water  as  unity. 
Since  water  dissolves  the  nitre,  mercury  is  used  instead. 
The  instrument  employed  is  called  a  mercury  densimeter, 
and  consists  of  a  glass  globe  a,  Fig. 
2,  connected  with  an  air-pump  by 
a  rubber  tube  c. 

The  globe  is  exhausted  of  air 
and  its  lower  end  immersed  in 
mercury  in  the  dish  d. 

The  mercury  is  allowed  to  rise 
till  it  fills  the  globe  and  stands  at 
a  certain  height  in  the  glass  tube 
€•.  The  globe  is  then  detached 
full  of  mercury  and  weighed.  It 
is  then  emptied,  and  a  given 
weight  of  powder  placed  in  it,  re- 
turned to  its  original  position,  the 
air  again  exhausted,  and  mercury 
allowed  to  enter  till  it  stands  at 
the  same  height  as  before ;  the 
globe  with  its  mercury  and  pow- 
der again  detached  and  weighed. 
The  difference  of  the  two  weights 
of  mercury  gives  the  weight  of  the  mercury  whose  volume 
is  equal  to  that  of  the  powder. 

Let  a  =  the  weight  of  the  powder; 

P  =  the  weight  of  the  vessel  and  mercury; 

P  =  the  weight  of  the  vessel,  mercury,  and  powder ; 


FIG.    2. 


4  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

S  =  the  specific  gravity  of  the  mercury  ; 
$  =  the  specific  gravity  of  the  powder. 

Then  P'  —  a  •=.  the  weight  of  the  mercury  and  vessel 
when  the  latter  is  partially  filled  with 
powder  ; 

p  —  P'  -|-  a  =  the   weight  of  the  volume  of   mercury 
displaced  by  the  powder. 

Since  the  weights  of  equal  volumes  are  proportional  to 
the  densities,  we  have 

a  :  P  -  P'  +  a  :  :  S  :  S, 

or 

aS 


The  density  varies  between  1.68  and  1.85. 

GRAVIMETRIC  DENSITY  is  the  name  given  to  the  density  of 
powder  when  the  spaces  between  the  grains  are  considered. 
That  is,  it  is  the  specific  gravity  of  the  powder  in  its  natural 
form.  Suppose  we  have  a  solid  piece  of  powder  weighing 
i  Ib.  If  we  determine  its  specific  gravity,  we  will  obtain  a 
value  d  given  by  formula  (i).  Suppose  the  same  powder 
broken  up  into  grains.  Its  weight  will  not  change,  but  its 
volume  will  be  greater  than  before.  If  we  determine  its 
specific  gravity  under  these  circumstances,  by  comparing  its 
weight  with  the  weight  of  an  equal  volume  of  water,  we  have 
a  particular  value,  called  the  "  gravimetric  density." 

It  is  evident  that  the  same  powder  will  have  only  one 
value  for  tf,  but  may  have  many  values  for  gravimetric  den- 
sity according  to  its  granulation.  If  the  shape  of  the  grain 
is  changed,  the  same  weight  of  powder  will  occupy  a  greater 
or  less  space  according  as  the  spaces  between  the  grains  are 
greater  or  less. 

Hence  we  say  that  gravimetric  density  measures  the  ca- 
pacity of  powder  to  pack,  or  measures  the  spaces  between 
the  grains. 

A  cubic  foot  of  powder  is  usually  taken  in  determining 


GUNPOWDER  AND    INTERIOR  BALLISTICS.  5 

gravimetric  density.     A  cubic  foot  of  water  weighs  62.425 
Ibs.     Hence  we  have 


w 
= 


y  denoting  the  gravimetric  density,  and  w  the  weight  of  a 
cubic  foot  of  powder,     y  varies  between  0.875  and  i.oo. 

The  space  actually  occupied  by  the  solid  powder  in  a 
Driven  volume  is  determined  as  follows  : 

o 

Let  V  •=  the  total  volume  occupied  by  the  powder; 

v  =  the  volume  of  the  solid  powder. 
Since  v6lumes  are  inversely  as  densities,  we  have 


*=r      ........    (3) 

If  Y  =  i-oo  and  *  —  '-8  (the  ordinary  values),  we  have 

.......    (4) 


That  is,  the  volume  occupied  by   the  solid   powder   in  a 
charge  is  about  .56  of  the  total  volume  of  the  charge. 

3.  Form  of  Grain. 

Irregular  Granulation.  —  The  processes  of  manufacture 
are  the  same  for  all  powders  up  to  and  including  incorpo- 
ration. 

If  the  mill-cake  be  pressed  into  slabs,  and  these  slabs 
broken  up  into  irregular  grains  by  rollers,  we  have  powders 
of  "  irregular  granulation."  In  our  service  the  powders  of 
irregular  granulation  are  : 

(a)  Small-arms  poivder,  used  in  the  Springfield  rifle  and 
carbine,  and  in  small  arms  generally,  and  also  as  a  bursting- 
charge  in  field-shells. 

(b)  Mortar-powder,  used  in  the  3.oo-inch  wrought-iron  rifle, 
in  the  siege  and  sea-coast  smooth-bore  mortars,  and  in  their 
shells. 

(c)  Cannon-powder,  used  in  the  old  8-  and  lo-inch  smooth- 
bore guns. 


O  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

(d)  Mammoth  Powder,  used  in  the  1  5-inch  Rodman  guns. 

(e)  I.  K.  Powder,  used  in  the  3.2O-inch  steel  B.  L.  rifle,. 
model  ^7/1885,  charge  (3.50)  Ibs. 

All  these  powders  may  be  regarded  as  having  grains 
which  approach  a  sphere  in  shape,  and  whose  mean  radius 
is  determined  as  follows: 

Let  N  =  the  number  of  grains  in  one  pound  of  powder  ; 
r  =  the  mean  radius  of  the  grain  in  inches  ; 
6  =  the  specific  gravity  of  the  powder. 
The  volume  of  one  grain  is 


(5), 
Its  weight  is  (Michie,  eq.  i) 

W=  VSg',  ........     (6) 

g'  being  the  weight  of  one  cubic  inch  of  water,  or 

62425 
1728  ' 

%nr*d  X  62.425  .  } 

1728 


Hence 


and  the  weight  of  N  grains  is 


N  W  =  X  62.425  X^  ( 

1728 

ButNW  =  i.     Hence 

*7tr*d  x  62.425  X  N 

1728 
or 

1.8766 


Using  this  method,  we  find 

2r  =  0.04  small-arms  powder  ; 
2r  =  0.08  mortar  powder  ; 
2r  =  0.30  cannon  powder; 
2r  =  0.75  mammoth  powder; 
2r  =  0.24  I.  K.  powder. 


GUNPOWDER   AND    INTERIOR   BALLISTICS. 


-a 


-a\ 


Regular  Granulation. — Powders  of  regular  granulation  are 
obtained  by  breaking  up  the  mill-cake  and  pressing  it  be- 
tween plates  having  depressions  in  them  of  regular  shape, 
such  as  a  sphere  or  a  pyramid. 

Under  this  head  we  have  the  Dupont  powders,  viz.; 

(a)  The  Hexagonal. — The  shape  of   the  grains  is  that  of 
two  hexagonal   pyramids   joined    base  to 

base.  The  grains  are  connected  by  a  thin 
cake,  which  is  broken  off,  and  leaves  a 
rough  surface  at  a,  which  facilitates  ig- 
nition. Used  in  the  8-inch  converted  rifle, 
charge  35  Ibs.  FIG.  3.— HEXAGONAL. 

(b)  The  Sphero-hexagonal,   Fig.  4,   which    is  the   same  as 

the  above,   except  that  spheres   are   substi- 
tuted for  hexagonal  pyramids. 

This  powder  is  now  used  for  all  the  field 
and  siege  guns  and  mortars.  In  the  field 
FIG.  ^SPHERO-  service  it  has  replaced  the  I.  K.  powder  used 
HEXAGONAL.  with  the  earlier  model  guns. 
Molded  Powder.— This  is  made  by  reducing  the  mill-cake 
to  powder  and  pressing  it  into  any  required  form,  each  grain 
being  made  separately ;  or  a  number  of  grains  of  powder  of 
irregular  granulation  may  be  compressed  into  a  single  large 
grain ;  the  latter  is  also  called  concrete  powder.  Under 
this  head  we  have  prismatic  or  brown  powder,  which  is  a 
molded  concrete  powder  made  as  above  described.  It  is 
called  brown  or  cocoa  powder  from  its  color,  which  is  due 
to  brown  charcoal. 

It  is  made  in  hexagonal  prisms,  Fig.  5,  about  I  inch  high 

and  1.375  inches  between  opposite ^^^ 

faces.  Each  prism  is  pierced  by  a 
central  hole  parallel  to  the  axis,  and 
about  0.40  inch  in  diameter.  The 
composition  is  generally  given  as 

Nitre 81.5  per  cent 

Charcoal 15.5  per  cent 

Sulphur 3.0  per  cent 


FIG.  5. — COCOA. 


IOO.O 


8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

It  is  a  slow-burning  powder,  and  is  used  in  modern  high- 
power  guns  of  large  calibre. 

4.  Inspection  and  Proof  of  Powder — History. 

INSPECTION. — The  object  is  to  see  that  the  powder  is 
properly  manufactured,  and  that  it  has  certain  required 
qualities. 

For  small-arms  powder  100  barrels  are  considered  a  lot, 
and  from  them  five  barrels  are  taken,  one  pound  of  powder 
from  each  barrel  being  selected  for  test.  If  the  test  is  suc- 
cessful, the  lot  is  accepted. 

For  Granulation. — All  grains  must  pass  through  a  sieve 
with  a  mesh  of  0.06  inch  and  none  through  a  mesh  of  0.03 
inch. 

Specific  Gravity  between  1.75  and  1.80  and  gravimetric 
density  between  0.96  and  i.oo. 

Dust  is  detected  by  allowing  a  stream  of  powder  to  fall 
rapidly  two  or  three  feet  in  a  strong  light.  There  must  be 
no  dust. 

Incorporation  is  tested  by  flashing  20  grains  of  powder  on 
a  copper  plate.  There  should  be  little  residue,  and  no 
globules  of  fuzed  nitre  on  the  plate. 

Moisture  is  determined  by  exposing  1000  grains  to  a  tem- 
perature of  100°  F.  for  24  hours.  The  loss  in  weight  should 
be  about  7  grains. 

Capacity  for  absorbing  moisture  is  tested  by  exposing 
1000  grains  to  the  vapor  of  water  for  24  hours.  The  gain  in 
weight  should  be  about  6  grains. 

Fouling  is  tested  by  firing  rapidly  100  rounds  of  rifle-ball 
cartridges  in  series  of  25  rounds  each  and  weighing  the  rifle 
after  each  series.  In  a  moderately  dry  atmosphere  the  weight 
of  fouling  from  the  100  rounds  should  not  exceed  15  grains. 

For  other  powders  the  inspection  will  vary  according  to 
the  terms  of  the  contract. 

PROOF. — The  object  of  proving  powder  is  to  ascertain  the 
initial  velocity  it  will  impart  to  the  projectile,  the  corre- 
sponding pressure  on  the  bore,  and,  for  small  arms,  the 
accuracy  of  the  projectile. 

The  powder  is  always  proved  in  the  gun  in  which  it  is 


GUNPOWDER   AND    INTERIOR   BALLISTICS.  9 

to  be  used,  and  with  service  charges.     The  velocities  and 
pressures  are  measured  with  instruments  to  be  described. 

HISTORY. — Gunpowder  was  first  used  in  Europe  early  in 
the  fourteenth  century,  and  in  the  form  of  powder  or  dust, 
whence  the  name.  The  guns  in  which  it  was  used  were 
weak,  and  the  powder  was  suited  to  them,  because  it  burned 
slowly  and  gave  low  pressures.  In  the  form  of  dust,  how- 
ever, it  was  difficult  to  load  at  the  muzzle,  as  cartridges  were 
not  used,  and  hence  loading  at  the  breech  was  introduced. 
This  failed  because  no  gas-check  could  be  devised  that 
would  completely  close  the  breech.  As  guns  improved  in 
strength,  better  results  were  obtained  by  graining  the  pow- 
der, but  the  grained  powder  became  too  strong  for  the  guns, 
and  large  guns  were  not  made.  No  marked  change  in  pow- 
der was  made  until  about  1860. 

General  Rodman,  of  the  Ordnance  Department,  then 
proposed  to  vary  the  size  of  the  grain  with  the  calibre,  using 
large-grained  powder  for  large  guns.  He  also  advocated  a 
perforated  powder,  which  was  not  used.  His  mammoth 
powder,  however,  was  adopted,  and  by  an  improvement  in 
the  process  of  gun-construction,  together  with  that  of  the 
powder,  he  built  smooth-bore  guns  up  to  20  inches  in  calibre. 

Following  Rodman's  plan,  various  forms  of  powder  have 
been  adopted  by  other  nations,  the  general  idea  being  to  so 
modify  the  action  that  the  gun  will  be  strained  less  at  the 
beginning  of  the  motion  of  the  projectile,  and  more  uni- 
formly throughout  the  bore,  than  with  the  old  powders. 
The  brown  powder  is  the  latest  development  of  the  old 
nitrate  powders.  It  has,  however,  many  objections,  and  at 
present  smokeless  powders  are  being  developed,  with  the 
prospect  that  they  will  supersede  the  others. 

5.  Combustion  in  Air — Laws. 

Explosion  is  the  rapid  conversion  of  gunpowder  into 
gases  and  solids  with  evolution  of  heat.  It  may  be  divided 
into  three  parts,  Ignition,  Inflammation,  and  Combustion. 

Ignition  is  the  setting  on  fire  of  a  part  of  the  grain  or 
charge,  and  for  this  purpose  a  temperature  of  300°  C.  is 
required. 


10  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Gunpowder  may  be  ignited  by  electricity,  by  contact 
with  an  ignited  body,  by  friction,  shock,  or  by  chemical 
reagents. 

A  gradual  heat  will  decompose  the  powder  by  subliming 
the  sulphur,  and  the  temperature  of  ignition  will  be  raised 
thereby. 

Flame,  owing  to  its  slight  density,  will  not  ignite  powder 
readily.  The  time  necessary  for  ignition  will  vary  with 
the  condition  of  the  powder.  Thus  damp  powder  ignites 
less  easily  than  dry  ;  a  smooth  grain  less  easily  than  a  rough 
one  ;  a  dense  grain  less  easily  than  a  light  one  ;  etc. 

Powder  is  ordinarily  ignited  by  a  primer,  by  electricity, 
or  by  contact  with  an  ignited  body. 

Inflammation  is  the  spread  of  the  ignition  from  point  to 
point  of  the  grain,  or  from  grain  to  grain  of  the  charge. 

With  small-grain  powders,  where  the  spaces  between 
grains  are  small,  the  time  of  inflammation  is  large  as  com- 
pared with  the  time  of  combustion  of  a  grain,  but  with 
modern  large-grain  powders,  the  facilities  for  the  spread  of 
ignition  and  the  time  of  burning  of  the  grain  are  so  great, 
that  the  whole  charge  is  supposed  to  be  inflamed  at  the 
same  instant,  and  the  time  of  inflammation  is  not  considered. 

Combustion  is  the  burning  of  the  inflamed  grain  from  the 
surface  of  ignition  inward  or  outward  or  both,  as  the  case 
may  be. 

LAWS.  —  Experiment  shows  that  powder  burns  in  the  air 
according  to  the  following  laws  : 

1.  In   parallel    layers,   with    uniform    velocity,  and  the 
velocity  is  independent  of  the  cross-section  burning. 

2.  The  velocity  of  combustion  varies  inversely  with  the 
density  of  the  powder. 

Hence  if  v  denote  the  velocity  of  combustion,  and  6  the 
density  of  the  powder,  we  have 


(10) 


the  constant  c  depending  on  the  nature  of  the  powder. 

3.  The  velocity  decreases  rapidly  as  the  degree  of  moist- 
ure in  the  powder  increases. 


GUNPOWDER  AND    INTERIOR  BALLISTICS.  II 

4.  It  increases  with  the  amount  of  trituration  of  the  in- 
gredients, up  to  a  certain  limit. 

5.  For  the  same  density,  trituration,  and  moisture,  the 
greatest  velocity  of  combustion  is  obtained  with  a  powder 
whose  composition  is  75  nitre,  15  charcoal,  and   10  sulphur. 

6.  In  air  the  actual  velocity  of  combustion  is  from  0.4  to 
0.6  inch  per  second. 

7.  The  velocity  varies  with  the  pressure  according  to  a 
law  which  is  expressed  by  the  following  formula  of  Sar- 
rau: 


•**• 


in  which  v  is  the  velocity  of  combustion  for  the  pressure 
/,  and  v0  the  velocity  in  open  air  corresponding  to  the  at- 
mospheric pressure  p0. 

According  to  this  formula,  a  powder  which  burns  0.6 
inch  per  second  in  air  would  burn  about  29  inches  per 
second  in  a  gun  .under  a  pressure  of  35,000  Ibs.  per  square 
inch. 

6.  Formula  for  Burning  in  Air  of  Grains  of  Different  Shapes. 

To  deduce  a  formula  for  the  amount  of  powder  burned 
at  the  time  ty  we  proceed  as  follows  : 

The  amount  burned  per  unit  weight  or  per  unit  volume 
at  any  time  /  wijl  evidently  be  a  function  of  /,  and  may  be 
represented  by  <t>(t).  Suppose  0(V)  to  be  developed  accord- 
ing to  the  ascending  powers  of  /,  with  constant  coefficients, 
which  are  to  be  determined.  We  may  then  write 


+  etc.),  .     .     .     .     (12) 


in  which  a,  A,  and  /*  are  constants  depending  on  the  form  of 
the  grain,  and  t  is  the  total  time  of  combustion  of  the  grain, 
and  hence  depends  on  its  size.  The  negative  sign  is  used  be- 
fore A.  because  the  sign  of  this  term  is  found  to  be  negative 
for  all  forms  of  grain  in  use.  It  is  required  to  find  values 
for  a,  A,  and  //  for  all  service  grains. 


12  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Spherical  Grain.  —  Let  r  be  the  radius  of  the  grain  ; 
v  the  velocity  of  combustion  ; 
r  the  total  time  of  combustion. 

The  original  volume  of  the  grain  is  f  Trr*.      At  the  end 
of  the  time  /  the  radial  distance  burned  over  is  vt,  and  the 
radius  remaining  unburned  is  r  —  vt.     Hence  the  volume 
unburned  at  the  end  of  /  is  f  n(r  —  z//)3. 
The  volume  burned  is  then 

|7rr3  -  ^n(r  -  */)',    ......     (13) 

or 


But 

*=        ........    05) 


and  substituting  for  -  in  (14)  its  value  from  (15),  we  have 


(16) 


The  expression  (16)  is  the  actual  volume  burned  at  the 
end  of  the  time  /.  It  is  composed  of  two  factors,  the  first 
being  the  original  volume  of  the  grain,  |  nr3,  and  hence  the 
second  factor  must  be  the  proportional  part  burned  ;  that  is, 
the  amount  burned  per  unit  of  volume,  or  per  unit  of  weight, 
in  the  time  /,  according  as  we  consider  volumes  or  weights, 
and  is  denoted  by  <f>(i).  Hence  for  this  particular  form  of 
grain  we  have 


or 


Comparing  this  with  the  general  development  in  equation 
(12),  we  see  that 

a  =         \=i       w  = 


GUNPOWDER  AND    INTERIOR  BALLISTICS.  1$ 

Since  all  powders  of  irregular  granulation  may  be  con- 
sidered as  spheres  whose  mean  radii  can  be  calculated  by 
equation  (9),  and  since  the  hexagonal  and  sphero-hexagonai 
may  also  be  so  considered,  these  values  of  a,  A,  and  ^  apply 
to  ail  such  powders. 

Values  of  #,  A,  and  jw  for  Other  Forms  of  Grain. — By  a 
similar  process  we  can  find  the  values  of  a,  A,  and  /*  for  all 
service  grains.  These  values  are  collected  in  the  following 
table. 


Form  of  Grain. 

a 

A 

n 

Spherical          ^ 

' 

Cubical 

•a 

I 

I 

Irregular           f  '  ' 

3 

granulation  j 

!  J-^-Lj, 

*  -f  y  +  *y 

xy 

1  +  •*  +y 

i+-*-+y 

Flat      v  —   1t 

I      1  •   2JC 

IX  -f  X9 

X* 

1      I      *.* 

I  -f-  2* 

1+2* 

Flat,  x  —  y  —  i  

2 

| 

A 

Pierced  cylinder  } 
Pierced  prism       > 

l4-ac 

X 

Q 

Cocoa                     ) 

i  +  x 

Pierced  cylinder;       } 
thickness  of  wall  >•  
half  of  height 

3, 

2 

I 

~3 

OL  OL 

In  this  table  ;tr  =  -Q,  y  —  — ,  in  which  for  the  parallelopi- 

/ 

pedon  a,  ft,  and  y  are  the  lengths  of  the  edges  of  the  grain, 
a  being  the  least  dimension  ;  also,  for  the  pierced  cylinder, 

x  =  — - — ,  in  which  r  is  the  exterior  and  r'  the  interior 

radius  of  the  cylinder,  and  h  its  height. 

By  substituting  for  a,  A,  and  /*  in  the  general  formula  (12), 
the  values  given  in  the  above  table,  the  amount  of  powder 
burned  per  unit  weight,  or  per  unit  volume,  for  any  of  the 
above-shaped  grains,  can  be  determined  ;  and  this  amount, 
multiplied  by  the  total  weight  or  volume,  will  give  the  total 
amount  burned  at  any  time  /. 


14  TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 

7.  Velocity  of  Emission  —  Spherical  Grain. 

This  is  the  rate  of  evolution  of  the  gas  of  gunpowder  ; 
that  is,  the  ratio  of  the  part  of  the  unit  of  weight  of  powder 
burned  in  a  small  interval  of  time  to  that  time. 
Considering  unit  weight,  let 

v  denote  the  velocity  of  combustion  ; 
5  the  total  surface  burning  at  any  time  t  ; 
8  the  density  of  the  powder. 

Then  vdt  is  the  space  passed  over  by  the  burning  surface 
in  the  time  dt,  Svdt  the  volume  burned,  and  Svddt  the 
weight,  the  value  of  gf  being  unity  for  French  measures.  Then, 
from  the  definition,  we  have  for  the  velocity  of  emission 

Svddt 
V=   -ft-  =  •»*  .......     (19) 

This  equation  shows  that  the  velocity  of  emission  de- 
pends upon  — 

1.  The  total  burning  surface  5; 

2.  The  velocity  of  combustion  v  ; 

3.  The  density  of  the  powder  d. 

But  it  has  been  found  by  experiment  that  in  air 

v8  —  c,  (see  equation  (10).) 

The  velocity  of  emission  in  air  depends,  therefore,  upon 
the  surface  burning,  and  this  surface  depends  on  the  form 
and  size  of  the  grain. 

We  may  obtain  another  expression  for  the  velocity  of 
emission  which  is  more  convenient  for  discussion,  as  fol- 
lows : 

The  proportional  part  of  powder  burned  per  unit  weight 
at  any  time  t  is,  as  we  have  seen,  a  function  of  /,  and  has 
been  expressed  by  0(/). 

The  proportional  part  burned  in  the  time  dt  is  </[0(/)], 
and  by  definition  we  have 


The  value  of  0(*)  lor  different  forms  of  grain  can  be  de- 
termined just  as  for  the  spherical  grain,  and  knowing  these, 


GUNPOWDER  AND    INTERIOR   BALLISTICS.  1 5 

we  can  determine  the  values  of  the  velocity  of  emission  for 
different  forms  of  grain.  It  is  evident  that  the  form  of 
grain  whose  velocity  of  emission  is  least  at  first  will  be 
most  advantageous,  since,  the  rate  of  emission  being  small, 
the  gas  will  be  given  off  gradually  at  first,  and  the  press- 
ure in  the  gun  will  increase  slowly,  and  give  time  for  the 
projectile  to  move  before  the  gun  is  overstrained. 

We  can  therefore  determine  what  form  of  grain  is  best 
calculated  to  give  the  lowest  pressure. 

FOR  SPHERICAL  GRAIN. — Differentiating  equation  (12) 
with  respect  to  /,  we  have 

~    I  4  4*  \ 

.      .      (20.) 


dt 

Substituting  for  a,  A,  and  p  their  values  for  the  spherical 
grain,  viz.,  a  =  3,  A=  !,/*  =  £,  we  have 


At  the  beginning  of  combustion,  when  t  =  o,  we  have 

,-fi 

and  at  the  end,  when  /  =  r, 

rj  =  o. 

8.  Velocity  of  Emission  for  Parallelopipedon  and  for  Pierced  Cyl- 
inder. 

FOR  PARALLELOPIPEDON. — Substituting  the  values  of  a, 
A,  and  JM  for  the  parallelopipedon  in  (20.),  we  have 


w  —  ""LTvyj  —  *  i  ~   i  j  \  ]    _  "\~  i  j   i  ~j )  ^_   I         *$xy 

i    ~  Jj.  _  V  I       „      I      ^.       —    ~ 

When  t  =  o,  we  have 

^ 
and  when  t  =  T, 


1 6  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

For  the  flat  grain  whose  thickness  is  one  half  its  other 
dimensions,  x  =  y  =  £.  Hence  for  this  grain  we  have  at 
the  beginning  of  combustion 


and  at  the  end 


or  the  velocity  of  emission  is  less  at  the  beginning  and 
greater  at  the  end  for  a  flat  grain  than  for  a  spherical  one. 

FOR  PIERCED  CYLINDER—  COCOA  POWDER.—  Substitut- 
ing the  values  of  a,  A,  and  /*  for  the  pierced  cylinder  in  (2O#)> 
we  have 

_dWfj\_l+*t  2*       /v 

—dT     ~r\     r+^Tj" 

When  /  =  o,  we  have 

?=l<I+4r); 
and  when  t  =  r, 


r  —  r' 
For  this  grain  x  =  —  -  —  .     If  x  =  -J,  as  in  the  case  of  the 

flat  grain,  the  thickness  of  the  walls  is  one  half  the  height,, 
and  we  have,  for  the  velocity  of  emission  at  the  origin, 


2r        r 
and  at  the  end, 

»-* 

Comparing  this  with  the  spherical  and  flat  grains,  we  see 
that  the  velocity  of  emission  for  the  pierced  cylinder  is  less 
at  the  beginning  and  greater  at  the  end  than  for  any  other 
form  of  grain.  Hence,  so  far  as  velocit}^  of  emission  is  con- 
cerned, this  is  the  best  form  of  grain,  and  is  the  one  now 
used  in  large  guns. 


GUNPOWDER  AND    INTERIOR  BALLISTICS. 

The  results  are  shown  in  the  following  table : 


Form  of  Grain. 

Velocity  of  Emission 
at  Beginning. 

Velocity  of  Emission 
at  End. 

Spherical            ) 
Irregular  grain  \  '  ' 

J3_ 

T 

0 

Flat  

2 

^5 

Pierced  cylinder  .  . 

T 

L5 

T 

r 

J>_ 

r 

9.  Size  of  Grain  —  Density—  Progressive  Powders. 

SIZE.  —  The  velocity  of  emission  depends  on  the  surface  in 
combustion,  and  this,  as  has  been  shown,  depends  on  the  form 
and  size  of  grain.  The  effect  of  form  has  been  discussed. 
To  show  the  effect  of  size,  suppose  we  have  two  charges  of 
the  same  weight,  composed  of  cubical  grains. 

Let  a   represent   the   edge   of   the   grains    in   the   first 

charge  ; 

2a  the  edge  of  the  grains  in  the  second  charge  ; 
N  the  number  of  grains  in  the  first  charge. 
The  surface  of  each  grain  in  the  first  charge  will  be 


and  the  total  surface  in  the  first  charge 


Since  the  weights  are  proportional  to  the  cubes  of  the 
edges  of  the  grains,  each  grain  in  the  second  charge  will 
weigh 

°  _  o 


times  as  much  as  those  of  the  first  charge,  and  hence  there 

N 

will  be  only  —  grains  in  the  second  charge. 
8 

The  surface  of  each  grain  in  the  second  charge  will  be^ 
(20?  X  6, 


1  8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERV. 

and  the  total  surface  in  the  second  charge 


or  the  total  surface  in  the  second  charge  will  be  only  one 
half  that  in  the  first;  and  since  the  velocity  of  emission 
depends  on  the  surface,  it  will  be  in  the  beginning  one  half 
that  of  the  first  charge. 

INFLUENCE  OF  DENSITY.—  Considering  a  single  grain,  if 
we  increase  its  density,  the  volume  remaining  constant,  we 
decrease  the  velocity  of  combustion  according  to  the  formula 

vd  =  c, 

and  hence  do  not  change  its  velocity  of  emission,  since 
77  =  Svd.  But  considering  a  given  weight  of  power,  if  we 
increase  the  density  of  the  grains  without  changing  their 
volume,  we  increase  the  weight  of  each  grain,  and  hence  de- 
crease the  number  of  grains  contained  in  this  weight.  This 
decreases  the  initial  surface  of  combustion  in  the  given 
weight,  and  hence  decreases  the  velocity  of  emission. 

Ordinarily,  for  slow  emission  we  increase  at  the  same 
time  both  the  size  and  the  density  of  the  grain.  The  limit 
of  increase  in  size  and  density  is  reached  when  the  grains 
cannot  be  consumed  in  the  gun  before  the  projectile  leaves 
the  bore. 

PROGRESSIVE  POWDERS.  —  For  this  reason  progressive 
powders  have  been  used.  A  progressive  powder  is  one 
which  burns  slowly  at  first,  and  afterwards  more  rapidly. 

The  Italian  Fossano  powder  is  an  example. 

The  larger  grains  are  in  the  form  of  a  cube,  each  com- 
posed of  small  dense  grains  united  by  a  lighter  powder. 

The  grain  burns  at  first  as  a  cube,  with  a  small  burning 
surface,  but  the  light  powder  which  unites  the  dense  grains 
soon  burns  out,  and  the  cube  is  then  broken  up  into  a 
number  of  dense  grains,  by  which  the  burning  surface  and 
the  velocity  of  emission  are  greatly  increased. 

The  same  progressive  principle  is  found  in  nearly  all 
powders.  With  molded  powders  and  those  of  regular 


GUNPOWDER   AND    INTERIOR   BALLISTICS.  ig 

granulation  the  surface  is  more  dense  than  the  interior, 
owing  to  the  method  of  manufacture,  and  hence  this  surface 
burns  more  slowly  than  the  interior.  In  the  molded  pow- 
ders especially,  the  ends  of  the  prisms  next  the  punches 
which  mold  it,  are  most  dense.  Even  in  ordinary  powders 
of  irregular  granulation  the  same  principle  applies. 

10.   Combustion  in  a  Close  Vessel— Chemical  Formula— Noble  and 
Abel's  Experiments. 

To  determine  the  chemical  composition  of  the  products 
of  exploded  gunpowder,  and  the  various  circumstances 
attending  its  combustion,  it  is  necessary  to  burn  it  in  a  close 
vessel,  and  collect  the  products  for  examination  and  analysis. 

CHEMICAL  FORMULA. — It  is  generally  admitted  that  no 
chemical  formula  will  exactly  represent  the  results  of  the 
combustion  of  gunpowder  under  all  circumstances,  since 
these  results  vary,  for  the  same  powder,  with  the  conditions 
under  which  it  is  fired. 

The  formula  generally  adopted  is 

4KNO3  +  C4  +  S  =  K2CO3  +  K3SO4  +  N4  +  2CO2  +  CO. 

According  to  this  formula  we  should  have  for  the  solids 
and  gases  of  the  exploded  powder  the  following  percentages 
by  weight : 

K,CO,  =  28.53  ) 
K9S04  -  35.96  L  Solids. 
64.49  ) 

N4  =  11.56 

>-  Gases. 


S=  18.17 
C0=    5.78 

35-51 


It  will  be  seen  later  that  the  percentage  of  solids  is  less, 
and  of  gases  greater,  than  the  above,  and  also  that  the  actual 
constituents  of  both  solid  and  gaseous  products  are  different. 

NOBLE  AND  ABEL'S  EXPERIMENTS.  —  Apparatus  and 
Methods. — Numerous  experiments  have  been  made  by  Count 
Rumford  (1792),  Bunsen  and  Schischkoff  (1859),  and  by 


20 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


Rodman  (1863),  upon  the  composition  of  the  products  of 
fired  gunpowder,  the  pressure  produced  by  the  gases,  etc. ; 
and  while  many  of  them  are  valuable,  their  results  are  not 
strictly  accurate,  owing  to  defective  apparatus  and  other 
causes. 

Captain  Noble  of  the  English  Army,  and  Sir  F.  Abel,  a 
chemist  of  the  British  War  Department,  made  a  series  of 
experiments  in  1874  and  a  second  series  in  1880,  which  are 
accepted  as  authoritative  on  this  subject. 

Apparatus. — The  apparatus  (see  Fig.  6)  was  a  strong  steel 
vessel  of  the  shape  shown,  capable  of  resisting  very  high 


n 


FIG.  6. 

pressures.  The  charge  of  powder  was  introduced  into  the 
vessel  through  an  opening  a,  which  was  then  closed  with  a 
tapering  screw-plug.  Besides  this  screw-plug  there  was 
another,  £,  carrying  a  crusher-gauge  d  for  measuring  press- 
ures, and  a  third  opening,  e,  was  for  the  purpose  of  drawing 
off  the  gases  for  analysis.  The  charge  was  fired  by  elec- 
tricity. 

Methods. — Different  powders  were  used  in  these  experi- 
ments, and  for  each  kind  of  powder  a  series  of  experiments 
was  made.  The  volume  of  the  explosion-chamber  being- 
constant,  the  quantity  of  powder  in  each  experiment  was 
varied,  starting  with  a  very  small  charge  and  proceeding 
till  the  chamber  was  filled.  The  maximum  charge  was 


GUNPOWDER  AND    INTERIOR   BALLISTICS.  21 

2.2  pounds  (i  kilogram).  The  results  of  all  the  experiments 
were  compared  in  order  to  deduce  the  general  laws  pertain- 
ing to  all  the  powders,  and  the  variations  due  to  particular 
kinds  of  powder,  form  of  grain,  density,  etc. 

11.  Density  of  Loading — Object  of  Experiments. 

DENSITY  OF  LOADING. — It  is  evident  that  the  amount  of 
powder  fired  in  a  given  volume  must  greatly  affect  the  re- 
sulting pressures. 

It  is  necessary,  therefore,  to  determine  accurately  the 
relation  between  this  quantity  and  the  space  in  which  it  is 
fired.  If  gunpowder  were  always  of  the  same  density,  and 
of  the  same  gravimetric  density,  we  could  compare  the 
volume  of  the  powder  with  that  of  the  space  containing  it. 
But  we  know  that  both  density  and  gravimetric  density 
vary,  and  hence  if  a  vessel  were  one  half  full  of  two  different 
kinds  of  powder,  while  the  volume  of  powder  in  the  two 
cases  would  be  the  same,  the  actual  weights  would  be 
different.  By  referring  to  gravimetric  density,  we  see  that 
the  weights  of  equal  volumes  of  powder  and  water  are 
very  nearly  equal ;  hence  we  compare  the  weight  of  the 
powder  fired  with  that  of  a  volume  of  water  which  will  fill 
the  chamber  in  which  the  charge  is  fired. 

This  is  called  "  density  of  loading,"  and  is  a  very  impor- 
tant ratio,  which  is  constantly  used  in  discussing  the  action  of 
gunpowder  in  guns  or  in  any  closed  vessel.  It  may  be  de- 
fined as  "  the  ratio  of  the  weight  of  the  charge  of  powder 
to  that  weight  of  water,  at  its  maximum  density,  which  will 
completely  fill  the  volume  in  which  the  charge  is  fired." 

To  determine  an  expression  for  it,  let 

A  —  the  density  of  loading : 
c3  =  the  weight  of  the  powder  in  pounds  ; 
C  =  the  volume   in  which   the   powder  is  fired   in   cubic 
inches. 

One  cubic  foot  of  water  weighs  62.425  Ibs.:  hence  one 
pound  of  water  occupies 

1728 

=  27.68  cubic  inches. 


62.425 


22  TEXT-ROOK  OF  ORDNANCE   AND    GUNNERY. 

The  number  of  pounds  of  water  that  will  fill  the  volume 
Cis 

C 
27.68' 

and  by  definition 

J  =  -A-  =  27-68t5.  ....      (2!) 

6  £7 


27X58 

French  Measure  of  Density  of  Loading.  —  In  the  metric 
system  the  weight  of  the  charge  is  expressed  in  kilograms, 
and  the  volume  of  the  chamber  in  litres  or  cubic  deci- 
metres. 

Since  a  litre  of  water  weighs  one  kilogram,  the  volume 
of  the  chamber  in  litres  expresses  at  once  the  weight  in  kilo- 
grams of  the  water  which  would  fill  it,  and  hence  the 
density  of  loading  is  obtained  simply  by  dividing  the  weight 
of  the  charge  by  the  volume  of  the  chamber.  Therefore 


OBJECT  OF  EXPERIMENTS.  —  The  object  of  the  experi- 
ments was  : 

1.  To  determine  the  nature  and  composition  of  the  pro- 
ducts of  combustion. 

2.  The  effect  of  varying  the  size  of  the  grain,  and  the 
density  and  composition  of  the  powder. 

3.  The  amount  of  heat  generated. 

4.  The  volume.  of  the  permanent  gases. 

5.  The  maximum  pressure  exerted  by  the  gases,  and  the 
laws  of  its  variation,  and  from  the  data  thus  obtained  to 
calculate  the  effect  in  the  bore  of  a  gun. 

12.  Results  —  Nature  and  Composition  of  Products. 

NATURE  OF  PRODUCTS.  —  In  these  experiments,  for  each 
kind  of  powder  the  density  of  loading  was  varied  by  varying 
the  weight  of  the  charge,  starting  with  a  density  of  0.05,  and 


GUNPOWDER   AND    INTERIOR   BALLISTICS.  2$ 

increasing  by  constant  increments  up  to  a  density  i.oo.  For 
the  latter  density  the  vessel  was  completely  filled  with  the 
powders  used.  The  products  were  found  to  consist  of  per- 
manent gases  and  solids.  Noble  and  Abel  supposed  the 
solid  products  to  be  liquid  at  the  temperature  of  explosion, 
and  to  be  diffused  in  a  finely  divided  state  throughout  the 
gases.  When  the  explosion  chamber  was  opened  after  the 
combustion  of  the  charge,  the  residue  was  found  collected 
at  the  bottom  in  a  solid  form.  The  mass  was  compact  and 
hard,  and  of  an  olive-green  color,  changing  to  black  on  ex- 
posure to  the  air.  The  volume  of  this  residue  when  cold  was 
about  0.3  the  original  volume  of  the  powder. 

To  ascertain  the  condition  of  the  residue  immediately 
after  the  explosion,  the  following  method  was  adopted. 

One  minute  after  the  explosion,  the  vessel  was  inclined 
quickly  at  an  angle  of  45°.  It  remained  in  this  position  45 
seconds,  and  was  then  returned  to  its  original  position. 
When  the  vessel  was  opened,  the  solid  products  were 
found  to  be  inclined  to  the  walls  at  an  angle  of  45°. 

From  this  it  follows  that  one  minute  after  the  explosion 
the  solid  residue  was  in  a  liquid  state,  and  45  seconds  after 
this  it  had  become  solid.  Moreover,  a  slight  crust  adher- 
ing to  the  walls,  and  which  had  been  partially  broken  by 
the  liquid  when  it  took  up  its  inclined  position,  showed 
that  the  solidification  had  begun  one  minute  after  the  explo- 
sion. 

The  effect  of  high  temperature  on  the  solid  residue  was 
tested  as  follows.  It  was  exposed  to  a  temperature  of 
1700°  C.  in  a  Siemens  furnace.  At  first  a  slight  efferves- 
cence appeared,  which  disappeared  immediately.  At  the 
end  of  the  experiment,  a  slight  volatilization  was  visible. 
When  the  crucibles  containing  the  residue  were  removed 
from  the  furnace,  and  allowed  to  cool,  the  increase  in  volume 
of  the  solid  products,  as  determined  by  marks  left  on  the 
walls  of  the  crucibles,  was  about  78  per  cent. 

COMPOSITION. — This  was  determined  by  chemical  an- 
alysis, and  was  found  to  be  as  follows  for  pebble  powder. 
The  results  differed  slightly  for  different  powders,  and  are 
the  percentages  by  weight. 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


K,CO,  -  33 
K3S04=    7 

K2S  =  10 

S=    4 

Various  =    2 


*  Solids. 


Various  =     i 


44 


That  is,  100  pounds  of  pebble  powder,  when  fired,  will 
give  56  pounds  of  solid  residue  and  44  pounds  of  gases. 
A  mean  of  the  results  from  all  the  powders  gave  57  pounds 
solids  and  43  pounds  gases.  That  is,  the  solid  residue  is  57 
per  cent  and  the  gases  43  per  cent  of  the  original  weight  of 
the  charge.  The  theoretical  reaction  gives  64.49  Per  cent 
solids,  and  35.51  gases. 

13.  Hesults — Effect  of  Variations  in  Powder — Amount  of  Heat 
Generated — Volume  of  Permanent  Gases. 

VARIATIONS.  — Slight  variations  in  size  and  density  of 
grain  were  found  to  have  very  little  effect  upon  the  composi- 
tion of  the  products  of  combustion,  and  no  effect  whatever 
upon  the  pressures.  Hence  the  pressure  in  a  closed  vessel 
is  independent  of  the  size,  form,  and  density  of  the  grain, 
and  depends  only  on  the  density  of  loading  or  the  quantity 
of  powder.  The  case  is  very  different  for  a  gun,  as  will  be 
seen  later. 

AMOUNT  OF  HEAT. — The  amount  of  heat  generated  by 
the  explosion  was  measured  by  immersing  the  steel  ex- 
plosion-vessel after  discharge  in  a  calorimeter  containing  a 
given  quantity  of  water  at  a  known  temperature,  and  noting 
the  rise  of  temperature  of  the  water. 

The  mean  result  obtained  was  that  705  units  of  heat  were 
given  off  per  unit  weight  of  powder  burned.  Now  if  the 
mean  specific  heat  of  the  products  of  explosion  were  accu- 


GUNPOWDER   AND    INTERIOR  BALLISTICS,  2$ 

rately  known,  the  temperature  of  these  products  at  explo- 
sion could  be  determined  by  the  formula 


in  which  Q  is  the  quantity  of  heat,  and  c  the  mean  specific 
heat  at  constant  volume.  But  this  value  of  c  is  not  known. 
It  is  known  that  the  specific  heat  of  the  solid  products 
increases  with  the  temperature,  but  the  law  of  increase  is 
unknown.  Bunsen  and  Schischkoff  found  from  their  experi- 
ments a  value  for  c  =  0.185.  From  this  we  should  have 


and 

T,  =  T  +  273  =  381  1  +  273  =  4084°  C. 

Noble  and  Abel  believed  this  value  to  be  much  too  large, 
for  the  following  reasons  : 

1.  The  specific  heat  of  the  solid  products  increases  with 
the  temperature,  hence  0.185  *s  too  small. 

2.  The  heat  measured  by  the  calorimeter  includes  all 
the  heat  absorbed  by  the  explosion-vessel,  as  well  as  that  of 
the  gaseous  products.     The  heat  absorbed  by  the  vessel  is 
taken  from  the  products  of  explosion,  and-  hence  lowers  the 
temperature  ;  therefore  705  is  practically  too  large. 

3.  A  piece  of  platinum  wire  was  enclosed  in  the  explo- 
sion-chamber,  and    when   the   chamber   was   opened   after 
explosion  the  platinum  showed  only  slight  signs  of  fusion. 
As  this  metal  fuses  completely  at  2000°  C.,  it  was  thought 
that  if  anything  approaching  a  temperature  of  4000°  C.  had 
been  attained  the   metal  would   have  been  entirely  fused. 
The  temperature  of  explosion  was  therefore  obtained  by 
calculation,  as  will  be  explained. 

VOLUME  OF  PERMANENT  GASES.  —  This  was  determined 
by  collecting  the  gases  in  a  gasometer,  and  observing  their 
volume  at  the  ordinary  atmospheric  temperature  and  press- 
ure, and  afterwards  reducing  this  volume  to  zero  centigrade. 

For  the  purpose  of  comparing  the  volumes  of  different 


26  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

gases  the  "  specific  volume  "  of  each  is  used.  For  ordinary 
gases  this  is  the  volume  occupied  by  a  unit  weight  of  the  gas. 
at  zero  C.  and  under  atmospheric  pressure.  For  gunpowder, 
it  is  the  volume  occupied  by  \hzgasfrom  unit  weight  of  powder 
at  the  above  temperature  and  pressure,  and  was  found  to  be 
280  times  the  original  volume  of  the  powder.  That  is,  the  gas 
from  i  kilogram  of  powder  occupies  at  zero  Centigrade  and 
under  atmospheric  pressure  a  volume  of  280  cubic  decimetres. 

14.  Results — Pressure  of  Gases — Formula. 

PRESSURE. — For  each  kind  of  powder  the  pressure  was 
measured  with  the  Noble  crusher-gauge,  for  all  densities  of 
loading  from  0.05  to  i.oo.  The  results  were  plotted;  the 
abscissas  being  the  densities  of  loading,  and  the  ordinates  the 
corresponding  pressures.  The  resulting  curve  gave  the  law 
connecting  abscissas  and  ordinates.  It  was  then  necessary  to 
deduce  the  equation  of  this  curve  so  as  to  express  analyti- 
cally the  law  connecting  density  of  loading  and  pressure, 
and  afterwards  to  compare  the  results  calculated  by  this 
formula  with  those  obtained  by  experiment. 

FORMULA. — To  deduce  the  formula  we  proceed  as  follows: 
The  experiments  had  shown  that  the  products  of  explosion 
were  partly  solid  and  partly  gaseous.  Hence  for  a  given 
volume  of  explosion-chamber,  it  is  evident  that  the  volume 
occupied  by  the  gases  at  the  moment  of  explosion  is  equal  to 
the  total  volume  of  the  chamber  minus  the  volume  occupied 
by  the  solid  products.  We  can  then  calculate  the  pressure 
due  to  this  volume  by  Mariotte's  and  Gay-Lussac's  laws. 

Let  7"0  be  the  absolute  temperature  of  the  products  at 
the  moment  of  explosion ; 

7",  the  actual  temperature  of  these  products ; 

P,  the  pressure  in  kilograms  per  square  decimetre  on 

the  walls  of  the  chamber  at  the  same  instant ; 
/0 ,  the  normal  atmospheric  pressure  (103.33  kilograms 
per  square  decimetre) ; 

V,  the  volume  in  cubic  decimetres  actually  occupied 
by  the  gases  at  the  moment  of  explosion,  corre- 
sponding to  the  pressure  P\ 


GUNPOWDER  AND   INTERIOR   BALLISTICS.  2J 

F0 ,  the  volume  in  cubic  decimetres  occupied  by  the 
same  gases  at  zero  Centigrade  and  at  /0  pressure ; 

c3,  the  weight  of  the  charge  in  kilograms ; 

z/0,  the  specific  volume  of  the  gases ; 

a,  the  volume  occupied  by  the  solid  residue  of  i 
kilogram  of  powder  at  the  temperature  of  explo- 
sion ; 

C,  the  volume   of   the  explosion-chamber   in  cubic 

decimetres. 

Then  we  have  (Michie,  equation  823),  from  Mariotte's 
and  Gay-Lussac's  laws, 


=  p  ,F0— - — (23) 

fmw  t\         IT  •>  I  V    «•)/ 

But 

273+7-=  Tt; 

hence 

f  =  *§ (24) 

or 


-  273^* 

Now 

Fo  =  GWO  , (26) 

and 


P      273   x  v9 

but 

-  =  constant —/". (28) 

Hence 

p=f% (29) 

Now  F,  the  volume  actually  occupied  by  the  gases,  is  the 
difference  between  the  volume  of  the  chamber  and  that  of 
the  solid  residue.  The  volume  of  the  solid  residue  is 


28  TEX'l-auUK    OF  ORDNANCE  AND    GUNNERY. 

and  hence 

V  —  C  —  aw  .........     (30) 

The  expression  for  density  of  loading  is  (see  22) 

A_™.      .    £•_» 
-  c.    ..  C-  j 

Substituting  this  value  of  C  in  (30),  we  have 

F=Ji-«/0, 
and  this  value  of  Fin  (29)  gives 


the  equation  required. 

15.  Discussion  of  Formula  (31). 

To  compare  the  results  of  this  formula  with  those  ob- 
tained by  experiment  it  is  necessary  to  know  a  and/.  These 
can  be  calculated  by  equation  (31)  by  taking  from  the  ex- 
periments two  values  of  A  and  the  two  corresponding  values 
of  P,  and  substituting  in  (31).  We  will  thus  have  two  equa- 
tions containing  the  two  unknown  quantities  a  and  f  from 
which  they  may  be  determined.  In  this  manner  Noble  and 
Abel  found  for  these  constants  the  following  values: 

/=  291200  kil.  per  sq.  dee.  =  18.49  tons  Per  scl-  inch. 
a  =  0.57. 

Taking  Noble  and  Abel's  numerical  values,  we  have  for 
the  French  units 

2QI200J 
"  I  -  0.57^' 

or  for  English  units 

......  (33) 


This  value  of  a  means  that  when  the  volume  of  the 
charge  is  i  cubic  decimetre  the  volume  of  the  solid  prod' 
nets  is  0.57  cubic  decimetre. 


GUNPOWDER   AND    INTERIOR   BALLISTICS.  2$ 

Referring  to  equation  (4),  it  is  seen  that  the  volume  of 
the  solid  residue  after  explosion  is  nearly  equal  to  that  of 
the  solid  powder  in  the  charge  before  explosion. 

If  the  charge  is  in  kilograms,  the  volume  of  the  solid 
products  is  obtained  by  multiplying  the  number  of  kilo- 
grams by  0.57.  If  the  charge  is  in  pounds,  the  volume  of 
the  solid  products  is  obtained  by  multiplying  the  number 
of  pounds  by  27.68  and  this  by  0.57,  or 

Vol.   of  solid  products  =  No.  Ibs.  X  27.68  X  0.57 ; 

=  No.  Ibs.  X  15  77- 

When  the  chamber  is  full  of  powder  the  density  of 
loading  for  the  powders  used  by  Noble  and  Abel  is  i.oo. 

In  this  case,  since  no  more  powder  can  be  introduced, 
we  should  get  the  greatest  possible  pressure  which  gun- 
powder will  give.  This  is  sometimes  called  the  "  absolute 
pressure."  Its  value  is  by  (33),  for  A  =  i, 

P=  43  tons  per  square  inch. 

16.  "  Force"  of  Powder — Temperature  of  Explosion. 

FORCE. — Assume  equation  (31), 


If  in  this  equation  we  make 

A 


(34) 
(34*) 

(35) 


Comparing  this  with  the  general  expression  for  density 
Of  loading, 

A  & 

"=€' 


3°  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

we  see  that  when  the  weight  of  the  powder  is  unity,  and 
the  volume  of  the  chamber  in  which  it  is  fired  is  (i  +  a)>  we 
have,  from  (34*2), 

p=f- 

The   quantity  represented   by  f  in  these  equations  is 
-see  28) 


and  is  constant.  This  value  of  /is  called  the  "  force"  of  the 
powder,  and  from  (340)  and  (35)  it  may  be  defined  as  "the 
pressure  per  unit  of  surface  exerted  by  the  gases  from  unit 
weight  of  powder,  the  gases  occupying  at  the  temperature 
of  explosion  a  volume  equal  to  unity."  The  volume  of  the 
chamber  is  i  +  a,  and  a  is  the  portion  occupied  by  the  solid 
products.  The  value  of  f  as  determined  by  Noble  and 
Abel  has  been  given. 

This  value  of  /  is  uncertain,  and  therefore  it  admits  of 
being  modified  to  account  for  various  resistances  in  a  gun 
which  cannot  be  readily  calculated. 

It  is  found  also  that  the  values  of  /for  different  powders 
are  nearly  the  same.  This  arises  from  the  fact  that  the 
quantity  of  heat  of  a  powder  varies  approximately  inversely 
as  the  specific  volume  of  the  gas  ;  and  by  (28)  the  product 
of  these  two  quantities  measures  the  force  of  the  powder. 

TEMPERATURE  OF  EXPLOSION.—  Assume,  (28), 


from  which 


We  have  found 

/=  291200 

v.  —  280  ; 
A  =  I03-33-. 


GUNPOWDER  AND    INTERIOR  BALLISTICS. 

Substituting  in  (36),  we  have 


and 


291200  X  273  8oQ 

103.33X280 

T  =2748  -273  =  2475°  C. 


These  values  agree  well  with  the  melting-point  of  plati- 
numr  and  could  be  accepted  if  there  were  no  doubt  about 
the  value  of/ 

COMBUSTION  IN  A  GUN— INTERIOR  BALLISTICS. 

17.  Action  of  Gunpowder  in  a  Gun. 

Suppose  we  have  a  charge  of  powder  which  completely 
fills  the  chamber  of  a  gun,  the  density  of  loading  being 
unity.  If  this  charge  be  completely  burned  before  the  pro- 
jectile moves,  we  obtain,  by  equation  (33), 

P  —  43  tons  per  square  inch. 


0      0'  0"     A 


FIG.  7. 


In  Fig.  7  let  O  be  the  position  of  the  base  of  the  pro- 
jectile before  firing,  OX  the  axis  of  the  bore,  and  OP  the 
axis  of  pressures.  Lay  off  OP  =  43  tons,  and  we  have  the 
pressure  corresponding  to  the  instantaneous  combustion  of 


32  TEXT-BOOK  OF  ORDNANCE  AND    GUNN,ERY. 

the  charge.  From  this  point  P  the  gas  will  expand  accord- 
ing to  the  hypothesis  adopted,  and,  acting  on  the  projectile, 
will  cause  it  to  move  rapidly  down  the  bore,  the  ordinates 
of  the  curve  Px  representing  the  pressures  at  correspond- 
ing abscissas  of  travel.  The  equation  of  this  curve  will  be 
deduced  later. 

Error  in  Supposition. — It  is  evident  that  the  assumption 
that  all  the  powder  is  consumed  before  the  projectile  moves 
cannot  be  true  in  practice.  As  soon  as  the  pressure  rises 
high  enough  to  overcome  the  resistance  of  the  projectile 
and  gun  to  motion,  they  will  both  move  in  opposite  direc- 
tions ;  but  for  the  present  we  will  consider  the  motion  of 
the  projectile  alone. 

Quick-burning  Powder. — Take  a  small-grained  powder  of 
cubical  form.  The  time  of  combustion  of  this  powder  is 
small,  and  its  velocity  of  emission  at  first  great,  as  has  been 
shown.  Let  OP'  represent  the  pressure  which  is  sufficient 
to  start  the  projectile,  and  suppose  the  powder  is  all  burned 
when  the  projectile  reaches  A.  Under  these  circumstances 
the  relation  between  the  pressures  and  the  travel  of  the 
projectile,  or  the  "  pressure  curve/'  will  be  represented  by 
a  curve  such  as  OP ' P"abx. 

Slow-burning  Powder. — Take  the  same  weight  of  charge  of 
cocoa  or  slow-burning  powder.  The  time  of  combustion 
is  comparatively  great,  and  its  velocity  of  emission  at  first 
small.  Let  OP'  represent,  as  before,  the  pressure  required 
to  start  the  projectile,  and  suppose  the  powder  all  burned 
when  the  projectile  reaches  B. 

The  pressure  curve  in  this  case  will  be  OP ' P'"bx  ;  and 
from  these  curves  we  may  deduce  the  following  conse- 
quences : 

a.  The  quick  curve  will  rise  above  the  slow  one  near  the 
origin,  because  the  volume  of  gas  given  off  in  the  same  time 
is  greater  with  the  quick  powder. 

b.  The  work  done  by  the  quick  powder  upon  the  pro- 
jectile is  greater  than  that  done  by  the  slow  powder,  be- 
cause the  area  under  the  quick  curve  is  greater  than  that 
under  the  slow  one. 

c.  The  quick  powder  strains  the  gun  more  than  the  slow 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  33 

one,  because  the  maximum  pressure  O'P"  >  O"P"f,  and  this 
maximum  pressure  is  what  determines  the  maximum  strain. 
That  part  of  each  curve  from  P'  to  a  and  b,  respect- 
ively, is  called  the  combustion  curve,  because  during  this 
time  the  powder  is  still  burning  and  giving  off  gas.  The 
part  from  a  and  b  to  x  is  called  the  expansion  curve,  be- 
cause from  these  points  on  the  gas  is  expanding  only. 

18.  Equation  of  Pressure  Curve — Noble  and  Abel's  Method. 

The  equation  of  the  true  pressure  curve  is  very  difficult 
to  deduce,  since  at  the  origin,  as  we  have  seen,  gas  is  being 
evolved  while  the  projectile  is  moving,  and  this  renders  the 
problem  very  complex. 

Noble  and  Abel  deduced  the  equation  of  the  curve  Pabx, 
Fig.  7,  under  the  following  hypotheses  : 

1.  That  all  the  powder  is  burned  before  the  projectile 
moves. 

2.  That  the  solid  products  of  combustion  give  off  heat 
to  the  gases  during  the  expansion. 

Let  £,  represent  the  specific  heat  of  the  solid  products, 
supposed  constant  throughout  the  expansion,  and  dT^  any 
small  change  of  temperature  of  the  products  of  combustion. 

Then  ctdT9  is  the  corresponding  quantity  of  heat  given 
to  the  gases  by  the  solid  products  per  unit  of  weight. 

Let  wt  represent  the  number  of  units  of  weight  of  the 
solid  residue-  then  the  total  quantity  of  heat  given  to  the. 
gases  by  the  solid  residue  is  wj^dT^.  Let  w^  be  the  number 
of  units  of  weight  of  the  gases.  These  gases,  by  hypothesis, 
receive  the  heat  above  found,  and  hence  they  receive  per 
unit  of  weight  a  quantity  of  heat  dQ  equal  to 


dQ=-      CldT.  =  -  ficJT.,  ....    (37) 


w, 


ft  being  the  ratio  — ,  and  the  negative  sign  being  used  since 

71,  is  a  decreasing  function  of  Q. 

When  the  volume,  pressure,  and  quantity  of  heat  of  a 
gas  change  at  the  same  time,  we  have  a  general  law  con- 


34  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

necting  them,  which  is  expressed  by  the  following  equation 
(Michie,  832): 


(38) 


m  which  dQ  is  the  elementary  quantity  of  heat  imparted  to 

the  gases  ; 
dp  and  dv  the  elementary  changes  of  pressure  and 

volume  of  the  gas  due  to  dQ  ; 
Cp  and  c,  the  specific  heats  at  constant  pressure 

and  volume,  respectively. 

Substituting  in  equation  (38)  for  dQ  its  value  given  by 
(37),  we  have 

—  ftc^T^  =  -^fvvdp  -\-  Cppdv) (39) 

This  equation  contains  T0  and  R,  while  the  equation  of 
the  pressure  curve  should  contain  only  /,  v,  and  constants, 
because  the  pressure  curve  is  one  showing  the  relation  be- 
tween/ and  v.  To  eliminate  T0  and  R,  assume  the  general 
equation  (823,  Michie)  connecting  the  pressures,  volumes, 
and  temperatures  of  a  gas. 

pv  =  RT0 (40) 

Differentiating,  we  have 

RdT.  =  pdv  -\-vdp, (40') 

from  which 

_  pdv  +  vdp 


Substituting  this  value  of  dT^  in  (39),  we  have 

-(A,  +  '4-  =  (^'  +  ^f (40") 

For  small  changes  of  pressure  and  volume  /?,  clt  cp,  and  cv 
are  constant.     Hence 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  35 

/.,  /,  z/,-,  and  v  being  the  initial  and  any  subsequent  values 
ot  /  and  v. 

Integrating, 


-*3 


Making 

w^=k' (42) 

we  have 

.  J' <43) 

the  equation  of  the  pressure  curve. 

19.  Application  of  Formula  (43)— Work  of  Gunpowder  in  a  Gun. 
APPLICATION. —  Assume  equation  (43) 

/.=. 

In  this  equation  vf  is  the  volume  occupied  by  the  gas  at 
the  moment  of  explosion,  and  pi  the  corresponding  press- 
ure. To  apply  this  equation  to  the  case  of  a  gun,  the 
original  volume  vt  occupied  by  the  gas,  is  the  volume  of  the 
chamber  in  which  the  charge  is  fired,  minus  the  volume 
occupied  by  the  liquid  products  of  the  charge.  The  volume 
it  occupied  by  the  gases  corresponding  to  the  pressure  p 
is  the  total  volume  to  which  the  gas  has  expanded,  including 
that  of  the  chamber,  minus  the  volume  occupied  by  the 
liquid  products. 

Hence  if  v'  denote  the  original  volume  of  the  chamber, 
the  density  of  loading  being  unity,  av'  is  the  volume  occupied 
by  the  liquid  residue,  and  v{  =  v'  —  av'  =  v'(i  —  a).  Also, 
if  v"  represent  any  subsequent  volume  of  the  bore,  at  which 
the  pressure  is/,  the  volume  actually  occupied  by  the  gas  is 

v  =  v"  -  av'. 
Making  these  substitutions  in  (43),  we  have 

(44) 


36  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Taking  from  the  experiments  the  values  of  the  constants, 
we  have 

pi  =  43  tons  per  square  inch  ; 

^=0.57;  ft  =  1.2957; 

^  =  0.2324;       ^=0.1762;       ^=0.45; 

k'  =  1.074, 
and  substituting  in  (44),  we  have 


(45) 


for  use  in  practice. 

WORK  OF  GUNPOWDER.  —  The  general  expression  for  the 
work  done  by  a  gas  expanding  from  a  volume  vt  to  a  volume 
v  is 


=    /   pdv. 
J*i 


W=    I    pdv (46) 

J*t 

Substituting  for  /  its  value  from  (44)  and  changing  the 
limits  to  v"  and  v'y  we  have 


or 


Integrating,  we  have 

' 


12  x  ( 

Multiply,  and  divide  the  second  member  by  \v'(i  —  a)Y'~l  : 

-       •     (49) 

12  is  used  to  reduce  to  foot-tons.     This  is  Noble  and  Abel's 
formula  for  work. 

Taking  the  volume  corresponding  to  the  muzzle  of  the 
gun,  the  corresponding  work  is  obtained.  If  there  were  no 
loss  of  energy  due  to  the  friction,  resistance  of  rifling,  etc., 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  37 

the  work  thus  calculated  should  be  equal  to  the  energy  in 
foot-tons  possessed  by  the  projectile  at  the  muzzle,  which  is 


2g  X  2240 ' 

w  being  the  weight  of  the  projectile  in  pounds,  and  V  its 
muzzle  velocity  in  feet  per  second.  But  E  is  always  less 
than  W,  owing  to  the  above  causes ;  and  the  ratio 


is  called  the  "  factor  of  effect  "  for  the  particular  gun  and 
charge. 

Knowing  this  factor  for  any  given  gun  we  can  find  the 
muzzle  velocity  for  a  given  charge  by  calculating  Wby  (49), 
multiplying  it  by  F,  and  we  have 


_-  =  FW 

2g  X  2240 

from  which 


(5o) 


Infinite  Expansion.  —  When  the  length  of  bore  becomes 
infinite,  v"  in  (49)  is  infinite,  and  we  have 

/X(i-«)  ,    , 

-    I2(k'  -  I)  ' 

Using  the  constants  as  given  above,  and  substituting  for 
v'  its  value,  27.68  cubic  inches,  the  volume  occupied  by  one 
pound  of  powder,  we  have 

W=  576.35  ft.-tons   ......     (52) 

for  the  work  of  one  pound  of  powder  expanded  to  infinity, 
under  Noble  and  Abel's  hypothesis. 

20.  Equation  of   Pressure  Curve  —  Recent  Hypothesis  —  Expression 

for  Work  under  this  Hypothesis. 

EQUATION  OF  PRESSURE  CURVE.—  In  recent  discussions 
Noble  and  Abel's  hypothesis  is  rejected,  as  it  is  believed  that 


38  TEXT-  BO  OK  OF  ORDNANCE  AND    GUNNERY. 

from  the  feeble  absorbing  power  of  gases  generally,  they  re- 
ceive only  a  very  minute  quantity  of  the  heat  radiated  by  the 
solid  products.  The  equation  of  the  pressure  curve  Pabx> 
Fig.  7,  is  therefore  deduced  under  the  following  hypotheses: 

1.  That  all  the  powder  is  burned  before  the  projectile 
moves. 

2.  That  the  gases  expand  without  receiving  heat  from  or 
giving  off  heat  to  any  external  source,  and  that  the  work 
done  on  the  projectile  is  due  to  their  own  heat  ;  that  is,  the 
expansion  is  adiabatic. 

Assume  the  equation  expressing  the  general  law  con- 
necting the  heat,  volume,  and  pressure  of  a  gas,  as  beforev 
(equation  832,  Michie's  Mechanics), 


R 

Since  no  heat  is  gained  or  lost  externally,  dQ  —  Q  and 
we  have 


Making  —  =  k  and  integrating  between  the  limits  pt 

£9 

and  v,  we  have 


(53> 

or 

rv>,~i* 

(54) 

which  is  the  equation  of  the  pressure  curve,  and  differs  from 
that  deduced  under  Noble  and  Abel's  hypothesis  only  in 
the  value  of  the  exponents  k  and  k'y  k'  being  1.074  and  k,  for 
powder  gases,  1.30. 

WORK. — To  deduce  the'  expression  for  work  in  this  case, 
we  have,  as  before,  equation  (46), 

r 

W  —    I    pdv. 


GUNPOWDER   AND    INTERIOR   BALLISTICS.  39 

Substitute  for  p  its  value  from  (54),  integrate,  and  we 
have 


(55) 


When  v  =  v{  we  have  W  =  o,  and  C  —  -~-  -  ;     hence 


w= 


21.,  Work  of  Gunpowder  in  Terms  of  Force  and  Weight  of  Charge 
—  Expression  for  it  in  Terms  of  Length  of  Travel  of  Projectile. 

WORK  IN  TERMS  OY  FORCE  AND  WEIGHT.  —  If  &  be  the 
weight  of  the  charge  in  kilograms,  the  initial  volume  occu- 
pied by  the  gas  from  each  kilogram  of  powder,  expressed  in 
cubic  decimetres,  will  be 

*>  =  ^ 

GO 

hence 

pM^ppfi;     ......    (57) 

and  from  Mariotte's  law  we  have 

p.v^  =  p"v"  =  C(a  constant), 

see  equation  (814),  Michie's  Mechanics. 

Now  if  we  make  v"  =  i  —  one  cubic  decimetre,  p"  be- 
comes by  definition  the  force  of  the  powder,  and  hence 

A",  =/"=/; 

and  from  (57), 

p&i^fco. 

*. 

Substituting  in  (56)  for/^,-  this  value,  we  have 


in   which    W  is   expressed  in  terms  of  the  "  force  of  the 
powder  "  and  its  weight. 

In  equation  (58)  the  force  of  the  powder  is  expressed  in 
kilograms  per  square  decimetre,  and  the  volumes  in  cubic 
decimetres.  Hence  the  work  W  will  be  expressed  in  kilo- 


40  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

gram-decimetres.  It  is  usual,  however,  to  express  work  in 
kilogram-metres,  and  this  is  done  by  dividing  by  10;  and  we 
have 

_  —  W  —         J \  T  —  1—  1          v  fcrri 

10 "       ~  io(£- 1)  l     \v>    r 

WORK  IN  TERMS  OF  LENGTH  OF  TRAVEL  OF  PROJECTILE. 
—We  can  place  this  expression  for  work  under  a  still  more 
convenient  form,  as  follows  : 

Reduced  Length  of  Initial  Air-space. — The  initial  air-space 
in  the  powder-chamber  is  equal  to  the  total  volume  of  the 
chamber  minus  the  volume  occupied  by  the  solid  powder; 
and  the  reduced  length  of  this  air-space  is  the  length  of  a 
cylinder  whose  volume  is  that  of  the  initial  air-space,  and 
whose  area  of  cross-section  is  that  of  the  bore  proper. 
To  determine  its  value, 

let  A  be  the  density  of  loading ; 
#,  the  density  of  the  powder; 
GO,  the  area  of  cross-section  of  the  bore ; 
2,  the  reduced  length  of  the  initial  air-space. 
We  have 

GO  CO 


The  volume  occupied   by  the  solid  powder  in  cubic 
decimetres  is 


hence  the  volume  actually  occupied  by  the  gases,  or  the 
initial  air-space,  is 

„        .      co      GO 


This  volume  divided  by  co,  the  area  of  cross-section  of 
the  bore,  gives  2  ;  hence 

GO  I  I  l\  ff-^ 

2  =  --—-/  .........       (DO) 

«AJ    d/ 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  41 

Having  this  value  for  z,  we  have  (see  page  29) 

Vi=G02'       V=Go(Z  +  x)y         .       .       .       .(6Q0) 

x  denoting  the  length  of  travel  of  the  projectile. 
Substituting  these  values  in  (59), 


^_^|I_(  -  y-i     .  B 


(61) 

Taking  k  =  1.3  and  /=  291,200,  we  have  the  constants 
which  enter  (61),  and  W  can  be  calculated  for  any  length 
of  travel  x  of  the  projectile.  When  x  =  oo ,  the  bore  be- 
comes infinite  in  length,  the  powder  expanded  to  infinity, 
and  (61)  becomes 


-— 

io(k  —  i)' 

Making  c3  =  i,  we  have,  for  the  work  of  one  kilogram  of 
powder  expanded  to  infinity  under  the  adiabatic  hypothesis, 

W'  =  97066  kil.-metres  per  kilogram, 
=  142.2  ft.-tons  per  pound. 

Comparing  this  with  Noble  and  Abel's  value  for  the 
work  of  one  pound,  viz., 

W  —  576.35  ft.-tons  per  pound, 

we   see  that  the  work  is   much  less  under  the  adiabatic 
hypothesis. 

"22.  Division  of  Work  of  Gunpowder— Velocity  of  Recoil. 

DIVISION  OF  WORK. — Having  the  value  of  the  total  work 
done  by  gunpowder,  it  is  required  to  find  how  much  of  this 
work  is  done  upon  the  gun  and  how  much  upon  the  pro- 
jectile, and  thence  to  deduce  values  for  the  velocity  of 
recoil  and  of  the  projectile. 

In  this  discussion  we  suppose  : 

1.  That  the  gun  recoils  freely. 

2.  That  gravity  and  resistance  of  the  air  can  be  neg- 
lected in  comparison  with  the  great  pressures  considered. 

Then  we  have,  from  mechanics : 


42  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

1.  The  total  energy  of  the  system  is  equal  to  the  total 
work  done  by  the  powder  upon  it. 

2.  Since  the  gun  and  projectile  move  in  opposite  direc- 
tions  with   equal   momenta,  the    sum   of  the  quantities   of 
motion  of  the  system  is  zero. 

The  energy  of  the  system  after  the  projectile  has  passed 
over  a  given  path  x  is  composed  of  three  quantities:  ist, 
the  energy  of  the  projectile ;  2d,  that  of  the  gun ;  3d,  that 

of  the  charge.  The  energy  of  the  projectile  is  -  — ,  m  de- 
noting its  mass  and  v  its  velocity  of  translation.  To  this 
should  be  added  the  energy  of  rotation ;  but  this  is  so  small 

MV'* 
that  it  may  be  neglected.     The  energy  of  the  gun  is , 

M  being  the  mass  and  v'  the  velocity. 

The  energy  of  the  charge  is  unknown,  since  the  velocity 
of  its  particles  is  unknown.  The  velocities  of  these  par- 
ticles vary  from  zero,  near  the  bottom  of  the  bore,  to  v, 
that  of  the  projectile,  for  those  in  contact  with  the  latter, 
not  taking  into  account  irregular  motions  which  also  exist. 
Hence  the  mean  velocity  of  the  particles  is  less  than 

that  of  the  projectile.     If  j*  be  the  mass  of  the  charge,  — 

would  be  its  energy  if  the  velocities  above  mentioned  were 
equal ;  as  they  are  not,  we  represent  the  energy  of  the 

charge  by  —  X  #,  0  being  a  coefficient  whose  value  is  be- 
tween zero  and  unity. 

We  have,  then,  as  a  first  equation, 

2lV=  mi?  +  Mv*  +  Spi? (62) 

The  momenta  of  projectile  and  gun  are  mv  and  Mv'. 
As  before,  the  quantity  of  motion  of  the  charge  is  not 
known ;  but,  reasoning  as  above,  we  may  represent  it  by 
tffiv,  and  its  sign  will  be  +>  because,  as  the  centre  of  grav- 
ity of  the  system  is  fixed,  the  greater  part  of  the  gaseous 
mass  moves  in  the  same  direction  as  the  projectile.  The 
second  equation  is  then 

mv  -f-  6' fAv  —  Mv'  =  o (63) 


GUNPOWDER  AND    INTERIOR  BALLISTICS.  43 

The  values  of  6  and  6'  are  found  by  analytical  methods 
to  be 


VELOCITY  OF  RECOIL.—  From  (63)  we  have 

,          m  _L  B'fJL 

-5 


Make  v  =  F  the  initial  velocity,  and  we  have  v'  —  V  ,  the 
velocity  of  the  gun  at  the  moment  the  projectile  leaves  the 
bore.  Making  0'  =  £,  and  replacing  masses  by  weights,  we 
have 

t+- 

V'  =  —p--V.   .......    (65) 

Experiment  shows  that  this  formula  gives  correct  values 
for  V  at  the  instant  the  projectile  leaves  the  bore,  suppos- 
ing the  gun  to  recoil  freely.  But  this  value  of  V  does 
not  represent  the  maximum  velocity  of  recoil  ;  in  fact,  it 
gives  only  about  three  fourths  of  the  maximum,  since  it 
applies  only  at  the  instant  the  projectile  leaves  the  bore. 
For  slow  powders  the  velocity  of  recoil  is  increased,  since 
the  gas  continues  to  act  upon  the  piece  after  the  projectile 
has  left  the  bore. 

The  subject  of  recoil  will  be  further  discussed  under 
Gun-carriages. 

23.  Velocity  of  Projectile—  Passive  Resistances—  Limit  of  Length  of 

Bore—  Influence  on  Velocity  and  Maximum  Pressures. 
VELOCITY  OF  PROJECTILE.  —  Substitute  the  value  of  vf 
from  (64)  in  (62),  and  we  have 


This  equation  gives  the  velocity  of  the  projectile  as  a 
function  of  the  work  of  the  powder.  The  third  term  in  the 
denominator,  being  generally  small,  may  be  omitted,  and 
we  have 

.....    (67) 


44  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

If  we  have  a  quick  powder,  and  suppose  it  all  burned 
before  the  projectile  moves,  we  may  substitute  for  W  in 
(67)  its  value  from  (61),  which  gives 


Making  x  =  u,  the  total  length  of  travel  of  the  projectile, 
becomes  the  initial  velocity,  and  we  have 


For  a  long  gun  u  would  be  large  and  — - —    small,  and 

z  -\-  u 

V*  would  become 

(68) 


The  value  of  /in  this  equation  must  be  found  by  experi- 
ment, to  compensate  for  the  erroneous  assumptions  made  in 
deducing  it. 

PASSIVE  RESISTANCES  are  those  due  to  the  forcing  of 
the  band  of  the  projectile  into  the  grooves  of  the  rifling, 
friction,  etc. 

Let  p  denote  the  work  done  against  these  resistances 
over  the  path  x.  In  equation  (62)  this  work  is  not  ac- 
counted for,  and  it  is  therefore  not  exact.  Introducing  it 
into  that  equation,  we  have 


2(  W  -  P)  =  mv*  +  Mv'*  +  fyizf;      ...     (69) 
and  in  equation  (67)  we  have  for  the  velocity 

......  <« 


GUNPOWDER  AND    INTERIOR  BALLISTICS.  45 

LENGTH  OF  BORE.— Although  the  value  of  p  is  unknown 
we  can  use  it  as  follows  :  Differentiate  (70),  v,  W,  and  p  being 
variable. 


v  m  -\- 


In  Fig.  8  let  OX  be  the  axis  of  the  bore  and  OP  that 


X 


of  pressures.  Suppose  the  bore  divided  into  elementary 
lengths  dx.  Then,  since  the  length  multiplied  by  the  con- 
stant area  of  bore  is  the  volume,  we  may  replace  dx  by  dv, 
the  increment  of  volume,  as  in  the  figure.  From  equation 

(46), 


and  each  of  the  small  areas  bounded  by  the  pressure  curve, 
the  ordinates,  and  dv  will  be  a  value  of  dW.  In  the  same 
way 

dp  =  Kdv, 

K  being  a  constant  and  equal  to  the  constant  pressure  be- 
tween projectile  and  rifling  multiplied  by  the  coefficient  of 
friction.  Since  K  and  dv  are  both  constant,  the  values  of 
dp  will  all  be  equal,  and  they  are  bounded  by  the  straight 
line  KK',  the  ordinates,  and  the  axis  of  X. 

As  the  projectile  moves  from  0  toward  X,  the'increment 


46  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

of  the  work  due  to  friction  remains  constant,  while  dW  de- 
creases and  tends  towards  zero,  since  /  constantly  decreases. 
There  is  some  point,  then,  such  as  m,  where 


or  dv  =  o.  This  value  of  X  will  be  greater  for  a  slow 
powder  than  for  a  quick  one,  because,  as  we  have  seen,  for 
equal  charges  the  slow  powder  gives  a  less  maximum  pressure, 
and  hence  we  can  use  larger  charges  of  slow  powder  without 
overstraining  the  gun  ;  and  as  these  large  charges  give  off 
more  gas,  the  pressure  is  kept  up  better  along  the  bore  than 
with  the  quick  powder,  or  the  values  of  p  are  greater  along 
the  bore,  dp  being  independent  of  the  nature  of  the  powder. 
When  the  point  m  is  reached  where  dv  =  o,  or  the  velocity 
of  the  projectile  ceases  to  increase,  the  limit  of  length  is 
reached. 

With  small  arms  this  limit  is  attained  more  nearly  than 
with  cannon  ;  and  the  above  reasoning  shows  that  slow 
powder  requires  longer  bores  than  quick  powder. 

INFLUENCE  ON  VELOCITY  AND  MAXIMUM  PRESSURE.— 
Equation  (70)  shows  that  the  passive  resistances  decrease  the 
initial  velocity  of  the  projectile  ;  but  this  is  not  always  the 
case.  Certain  passive  resistances,  such  as  the  resistance  of 
the  rifling,  produce  at  first  a  more  rapid  combustion  of  the 
powder  on  account  of  the  rise  in  pressure  due  to  the  delay 
of  the  projectile  in  moving  off.  Hence  the  powder  acts  as 
a  quicker  powder,  the  work  done  by  it  over  a  given  path  is 
increased,  and  this  increase  of  work  may  more  than  com- 
pensate for  the  resistance.  It  follows  as  a  consequence 
that  the  maximum  pressure  on  the  gun  is  increased.  An 
accidental  resistance,  such  as  wedging  of  the  projectile, 
may  cause  a  great  increase  in  pressure,  and,  if  it  cannot  be 
overcome,  may  burst  the  gun. 

24.  Sarrau's  Formulas  —  General  Equation  of  Motion  of  Projectile 

in  Bore. 

The  formulas  deduced  above  furnish  approximations  to 
the  initial  velocity  of  the  projectile,  but  are  not  exact  for 
many  reasons.  Among  these  are  : 


GUNPOWDER   AND    INTERIOR   BALLISTICS.  47 

ist.  The  powder  is  supposed  to  be  all  burned  before  the 
projectile  moves.  This  is  known  to  be  incorrect. 

2d.  No  account  is  takeii  of  the  passive  resistances. 

3d.  The  kind  of  powder  and  the  calibre  of  the  gun  are 
not  considered. 

For  these  reasons  it  was  customary  to  use  empirical  for- 
mulas. These  formulas  gave  good  results  so  long  as  the 
conditions  under  which  they  were  deduced  were  not  de- 
parted from,  but  they  were  limited  in  their  applications  and 
could  not  be  generally  used. 

To  obviate  these  difficulties,  the  subject  has  been  dis- 
cussed by  M.  Emile  Sarrau,  a  distinguished  French  engineer 
of  powders,  etc.  In  his  discussion  the  following  hypotheses 
are  adopted  : 

1.  The  inflammation  of  the  charge  is  instantaneous. 

2.  The  gases  expand  adiabatically. 

3.  The  powder  is  not  all  burned  before  the  projectile 
moves. 

EQUATION  OF  MOTION.  —  At  the  end  of  any  time  /  let 

q  be  the  weight  of  powder  burned  ; 
x,  the  length  of  bore  passed  over  by  the  projectile  ; 
pl  ,  the  mean  pressure  ; 

vl  ,  the  volume  of  the  bore  in  rear  of  the  base  of  the  pro- 
jectile,  minus  the  volume  occupied  by  the  solid 
residue  of  the  powder  ; 
v,  the  velocity  of  the  projectile. 

The  gas  which  is  formed  at  the  time  /  expands  adiabati- 
cally, and  we  have,  for  any  time  t'  after  t  (see  equation  54), 


(72) 


/  and  v'  being  the  mean  pressure  and  volume  at  the  time 
/',  and  k  the  ratio  of  specific  heats. 

The  total  quantity  of  work  done  up  to  the  time  t'  is,  from 

(46), 


48  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY.. 

Substitute  for  /'  its  value  from  (72),  integrate,  and  we- 
ll ave 


(73) 


To  find  the  value  of  the  constant :  When  t'  =  /,  we  have 
v'  •=.  vl ;  and  if  we  consider  the  energy  of  the  projectile 
alone,  W  =  \mv*\  hence 

C  =  \mv*  +  ,  '  f  , 

K  —    I 

and  consequently 


-  k 


if-      -     -     (74) 


If  we  now  suppose  the  bore  to  be  infinite  in  length,  z/ 
becomes  infinite,  and  W7  becomes,  from  (61), 

fq     - 


"  io(k-  i)' 
and  since  k  >  I, 


k-  i 
becomes  zero.     Hence 


25.  Transformation  of  Equation  (75).  —  Errors  in  its  Deduction  and 

their  Correction. 

TRANSFORMATION.  —  Equation  (75)  is  transformed  as  fol- 
lows :     Make 

dx 
V  =  dt> 

vl  =  GO(Z  -f-  x)  ;     (see  equation  6oa  ;) 


This  last  equation  expresses  the  fact  that  the  total  press^ 
ure  on  the  projectile,/,^,  is  equal  to  the  accelerating  force,. 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  49 

While  this  is  not  exactly  true,  it  is  sufficiently  accurate, 
and  can  be  corrected  for,  as  will  be  explained. 

Making  these  substitutions  in  equation  (75)  and  including 
the  constant  10  in/,  which  is  equivalent  to  changing  the 
unit  in  which  the  force  of  the  powder  is  expressed,  we  have 

fq     _  mfd^V*      d*x  z-\-  x 
k  —  i  "  "   2  \dt  i  ~     n  d?  k  —  i*    "     '     '     ^ 

ERRORS  AND  CORRECTIONS. — In  deducing  this  equation 
certain  errors  have  been  made.  These  are : 

1.  The  total  work  which  a  weight  of  powder  is  capable 

of  doing,  when  expanded  to  infinity,  is  not  equal  to  j~- — ,, 

K  -~  I 

because  part  of  the  heat  is  absorbed  by   the  walls  of  the 
bore,  and  no  allowance  has  been  made  for  this  loss. 

On  the  contrary,  we  have  supposed  an  adiabatic  expan- 
sion without  gain  or  loss  of  heat.  Hence  -7— —  is  too  large 

K  —    I 

and  must  be  diminished. 

2.  At  any  time  /  the  work  of  expansion  is  not  equal  to- 
•Jm^2,  but  is  equal  to  the  total  energy  of  the  system,  includ- 
ing gun,  projectile,  charge,  and  gun-carriage. 

To  correct  for  this  we  must  increase  the  term  \m\- 


3.  We  have  assumed  /,<*>  =  w-^-,  or  that  the  total  press- 

ure on  the  projectile  is  equal  to  the  accelerating  force. 

This  is  not  correct,  because  the  force  pja  not  only  pro- 
duces acceleration  of  the  projectile,  but  overcomes  the 
passive  resistances,  such  as  forcing  of  the  band,  friction,,  etc- 

d*x 
Hence,  in  order  to  make  pja  —  m~~y  we   must   increase 


Instead  of  correcting  each  term  of  equation  (76)  as  in- 
dicated, we  can  apply  such  a  correction  to  the  first  member 
as  will  make  it  a  true  equation.  The  numerical  value  of  / 
is  uncertain,  and  we  may  therefore  apply  all  the  corrections 


1>O  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

to  this  quantity,  and  /then  becomes  a  numerical  coefficient 
Avhose  value  must  be  determined  by  experiment. 

26.  Deduction  of  Final  Equation  of  Motion  of  Projectile  in  Bore. 

Value  of  q.  —  The  method  of  determining  the  value  of/ 
in  equation  (76)  has  been  explained.  It  is  necessary  now  to 
find  the  value  of  ^,  the  quantity  of  powder  burned  at  the 
end  of  any  time  /. 

The  proportional  part  of  powder  burned  in  air  at  any 
time  /  is  given  by  the  general  expression,  (12), 

-       +        +  etc--      .     .     .     (77) 


By  multiplying  this  expression  by  the  volume  of  the 
grain  or  charge  we  obtain  the  volume  burned  (see  equation 
(16)  )  ;  and  multiplying  the  same  expression  by  the  weight, 
we  have  the  weight  burned  at  any  time. 

Hence,  GO  being  the  weight  of  the  charge,  we  have 


q  =  £0W  ........   (78) 

But  the  expression  (77)  applies  to  the  burning  of  a  grain 
or  charge  in  air.  In  a  gun,  the  pressure  varies  and  is  much 
greater  than  in  air,  and  hence  the  velocity  of  combustion 
varies  and  is  much  greater,  as  has  been  shown;  and  this 
variation  of  velocity  is  expressed  by  Sarrau's  formula 
already  given  (equation  n), 


(79) 


and  the  expression  for  <p(t)  must  be  modified  accordingly. 

Spherical  Grain.  —  Take  the  simplest  case,  that  of  a  spheri- 
cal grain.  When  burning  in  air,  we  have  found  for  the  vol- 
ume burned  at  any  time  t,  equation  (13), 


Since  v  is  no  longer  constant,  owing  to  the  variation  of 
pressure  in  the  gun,  the  space  burned  in  the  time  dt  is  vdt\ 


GUNPOWDER  AND    INTERIOR   BALLISTICS.  $1 

/»< 
vdt,  instead  of  vtt  as  in  the  case  of 

constant  pressure.  The  above  expression  for  the  volume 
of  powder  burned  in  the  case  of  a  spherical  grain  under 
varying  pressure  becomes,  then, 


(8o) 

and  the  value  of  0(/)  in  equation  (14)  becomes 

{         i    rf      \3 
0(0  =i-(i-  ~Jo  vdt] (81) 

If  in  this  equation  we  substitute  for  v  its  value  from  (79), 
we  have 


*«=i-     --:.!  \&}#\>  •  •  •  (82) 

Now 


r 
r  =  —, 


the  time  of  combustion  of  the  grain  in  air  under  the  normal 
pressure,  and 


Substituting  in  (82),  we  have 


Comparing   this   value   of   0(0   with   that  for  uniform 
pressure,  which  is,  equation  (17), 


(84) 

we  see  that  the  only  difference  is  the  substitution  of 


(orr. 


52  TEXT-BOOK  Of   ORDNANCE  AND    GUNNERY. 

Following  the  same  method  for  other  forms  of  grain,  the 
same  results  will  be  obtained.  Hence  we  conclude  that  if 
the  combustion  of  powder  under  constant  pressure  is  repre- 
sented by 


=  f(i  -*£+>£+  etc.), 


the  combustion  under  variable  pressure  will  be  represented 


FINAL  EQUATION. — In  equation  (85)  make 

/  =pl  the  mean  pressure  at  the  time  /. 
P^GD  =  *#-T-3-  (see  equation  (75#)). 
Whence 

A  =  vW' 
and  we  have  for  the  value  of  the  term  J  r^J  dt, 


and  substituting  this  value  in  (85),  we  have 


and  for  the  value  of  <7, 

q  =  c»0(/)  =  (3  X  2d  member  of  equation  (87).  .     (88) 
In  equation  (76)  make 


and  it  becomes 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  53 

Substituting  in  this  equation  the  value  of  q  from  (88),  we 
have  the  final  equation  desired,  which  is 


(        \l  m\*  rtfd'xV,,  , 

i  l~r    )  X  b)  *+ 


,  , 

x  l~r  *       -   J  +etc 

27.  Integration  of  Equation  (90)—  Practical  Formulas  for  Velocity 
and  Pressure—  Values  of  A  and  ^—Characteristics  a  and  /3. 

INTEGRATION.  —  Equation  (90)  must  be  integrated  before 
it  can  be  used  practically.  Sarrau  has  done  this  by  the  use 
of  auxiliary  functions  which  are  numerical  and  independent 
of  the  variable  elements  of  fire.  As  a  final  result  of  his 
process,  the  general  values  for  velocity  and  pressure  are 
expressed  in  the  form  of  definite  series,  which  are  very  con- 
vergent. On  this  account  it  is  necessary  to  consider  only 
two  terms  of  the  series  in  the  expression  for  the  velocity, 
and  only  one  term  in  the  expression  for  the  pressure. 

BINOMIAL  FORMULA  FOR  VELOCITY.  —  Considering  the 
two  terms  of  the  series,  Sarrau's  formula  for  velocity  is  ex- 
pressed as  follows.  It  is  called  the  binomial  formula  for 
velocities,  and  is  the  result  of  the  integration  of  equation 
<9o)  : 

(9D 


in  which  z>  is  the  velocity  of  the  projectile  at  the  point  », 
and  becomes  the  muzzle  velocity  when  u  is 
equal  to  the  total  length  of  travel  of  the  pro- 
jectile in  the  bore  ; 

u,  the  length  of  bore  passed  over  by  the  base  of 
the  projectile  in  inches,  measured  from  the 
position  occupied  by  it  before  firing.  In 
equation  (90)  this  length  is  denoted  by  x,  and 
is  changed  to  u  in  formula  (91)  ; 

*,  the  calibre  or  diameter  of  the  bore  in  inches  ; 

/,  the  weight  of  the  projectile  in  pounds  ; 

(5,  the  weight  of  the  charge  of  powder  in  pounds  ; 

A,  the  density  of  loading  ; 


54  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

a  and  ft,  two  coefficients  depending  on  the  nature  of  the 
powder  used,  and  called  the  "characteristics" 
of  the  powder; 

A  and  B,  two  numerical  coefficients  which  are  independ- 
ent of  the  elements  of  fire. 

The  values  of  a  and  ft  are 


in  which  /is  the  force  of  the  powder; 

a  and  A,  coefficients  depending  on  the  form  of  the  grain 
of  powder,  and  whose  values  for  the  different 
forms  of  grain  have  been  given  ; 
r,  the  total  time  of  burning  of  the  grain  in  air. 

FORMULA  FOR  MAXIMUM  PRESSURE  ON  BASE  OF  PRO- 
JECTILE. —  In  the  same  way,  as  the  result  of  integration,  the 
expression  for  the  maximum  pressure  on  the  base  of  the 
projectile  is 


(93) 


in  which  the  quantities  are  the  same  as  before,  and  K  is  a 
constant  whose  value  is  to  be  determined  as  will  be  ex- 
plained. 

VALUES  OF  A  AND  B.  —  If  for  a  given  powder  we  know  the 
values  of  a  and  ft,  we  can  fire  this  powder  from  two  differ- 
ent guns,  and  measure  the  resulting  initial  velocities.  This 
will  give  v.  The  values  of  c,  u,  and  p  are  known  for  the 
two  guns,  and  the  values  of  c3  and  A  also,  and,  having  two 
equations  containing  A  and  B,  they  can  be  calculated.  But 
it  is  difficult  to  find  exact  values  for  a  and  ft,  since  they  de- 
pend on  /and  r,  equation  (92),  and  the  values  of  these  quan- 
tities are  uncertain.  To  avoid  this  difficulty,  Sarrau  adopts 
a  particular  powder  which  he  calls  a  type  powder,  and 
assumes  for  it  the  values  /=  i,  t  •=.  i. 

The  values  of  a  and  A  for  the  type  powder  are  calculated 
as  explained  previously.  Hence  all  the  quantities  in  (91) 
are  known  except  A  and  B,  and  they  can  now  be  calculated. 


GUNPOWDER  AND    INTERIOR  BALLISTICS.  55 

Since  A  and  B  are  constants  to  be  determined  experimen- 
tally, whatever  errors  we  make  in  assuming  the  values  of  / 
and  r  will  be  corrected  for  in  the  values  of  A  and  B  as  found 
by  experiment ;  and  since  these  values  of  A  and  B  are  inde- 
pendent of  all  the  elements  of  fire,  they  will  be  true  for  all 
powders  and  all  guns.  A  and  B  are  found  by  experiment  be- 
cause they  depend  on  v,  which  is  determined  by  experiment. 

In  this  way  Sarrau  found  the  values  of  A  and  B  to  be 

log  A  =  2.56635  ; 
log  B  =  2.30964. 

CHARACTERISTICS  a  AND  (3. — Having  the  values  of  A  and 
B  in  (91),  we  must  know  the  characteristics  a  and  ft  for  any 
powder  before  we  can  apply  the  formula  to  this  powder. 
The  values  of  a  and  ft  depend  on  /,  a,  A,  and  r  (see  (92) ). 
a  and  A  can  be  calculated,  as  before  explained,  for  any  grain 
of  ordinary  shape,  and  their  values  for  most  service  forms 
have  been  given.  The  value  of /is  uncertain,  and  therefore 
for  simplicity  Sarrau  assumes  /  =  i  for  all  powders,  the 
same  as  for  the  standard  powder. 

We  have  seen  that/  is  practically  constant  for  all  pow- 
ders, and  hence  the  above  assumption  may  be  made.  The 
value  of  r  cannot  be  accurately  determined  except  by  the 
use  of  a  formula  not  yet  deduced,  and  hence  the  method  of 
determining  it  will  be  explained  later. 

28.  Maximum  Pressure  on  Breech  of  Gun— Value  of  K. 

MAXIMUM  PRESSURE.— Equation  (93)  gives  the  maximum 
pressure  on  the  base  of  the  projectile,  and  in  order  to  use 
it  K  must  be  known.  If  we  could  measure  accurately  the 
pressure  on  the  base  of  the  projectile,  the  value  of  K  could 
be  found  by  firing  a  shot  from  a  gun,  since  all  the  quantities 
except  K  in  (93)  would  be  known,  and  hence  it  could  be 
determined.  But  this  pressure  cannot  be  accurately  meas- 
ured, and  hence  we  determine  first  the  maximum  pressure 
on  the  breech. 

To  do  this  assume  equation  (64) : 


56  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Differentiate  with  respect  to  t  : 

dv'  _  m  +  #'/*  dv 
~dt'~      ~~M~~~dt' 

M 
Multiply  both  members  by  —  ,  co  being  the  area  of  cross- 

section  of  the  bore  : 

M  dv' 


.....    (95) 


Now  denoting  by  P0  the  maximum  pressure  per  unit  of 
surface  on  the  bottom  of  the  bore,  and  by  P  the  correspond- 
ing pressure  on  the  base  of  the  projectile,  we  have 


and  substituting  in  (95), 

(97) 


Substituting  weights  for  masses,  and  for  0'  its  value  i, 

(98) 


This  equation  does  not  give  true  values  for  P0  ,  since  in 
placing  the  total  pressure  equal  to  the  accelerating  force, 
equation  (96),  we  have  evidently  neglected  the  force  neces- 
sary to  overcome  the  passive  resistances.  Sarrau  has  there- 
fore adopted,  as  more  nearly  agreeing  with  experiment,  the 
following  formula  : 


GUNPOWDER  AND    INTERIOR  BALLISTICS.  57 

Substituting  for  Pin  (99)  its  value  from  (93),  we  have 

*=4+l|)^.  .  .  .  (ioo) 

Making 


we  have 


Making 

KK'  =  K0 
and 


which  is  justified  by  experiment,  w  have  finally,  for   the 
pressure  on  the  breech, 


or  reducing, 

P,  =  KffJ        .....         .    .    (103) 

Since  we  can  measure  very  accurately  the  pressure  on 
the  breech  of  a  gun,  we  fire  with  a  given  powder,  measure 
this  pressure,  substitute  it  for  P9  in  (103),  and,  as  all  the 
other  quantities  except  K0  are  known,  we  thus  obtain  its 
value,  which  is 

log  K*  =  4-25092. 

VALUE  OF  K  IN  (93).—  Having  the  value  of  P0,  we  substi- 
tute it  in  (99)  and  find  the  corresponding  value  of  P.  This 
value  of  P  in  (93),  together  with  the  known  values  of  the 
other  quantities,  will  give  K,  whose  value  is 

=  3.96197. 


58  TEXT-BOOK  OF  ORD  NANCE  AND    GUNNERY. 

Collecting   the  pressure  formulas  for  convenience,  we 
have 

P  =  Ko?A^  ,  on  base  of  projectile 


Pt  =  Kjx*At--^-,  on  breech  of  gun. 

log  K=  3-96l97; 

log  K,  —  4.25092. 

29.  Theoretical  Maximum  Velocity  —  Time  of  Burning  Correspond- 

ing to  the  Maximum  Velocity. 

MAXIMUM  VELOCITY.  —  Assuming  the  binomial  formula 
for  velocity,  and  replacing  a  and  ft  in  it  by  their  values, 
equation  (92), 


we  have 

/AA'          "IUr-**=n  (I04) 


If  in  this  equation  we  make  v  and  t  the  only  variables,  it 
can  be  shown  by  the  usual  rules  of  calculus  that  v  will  have 
a  maximum  value  for  a  particular  value  of  r.  That  is,  as 
i  decreases  in  value,  v  will  increase  till  it  reaches  a  maxi- 
mum. 

But  this  ought  not  to  be  the  case,  because,  theoretically, 
as  t  decreases,  or  the  powder  becomes  more  quick,  v  should 
increase;  and  this  increase  should  continue  up  to  the  limit 
where  the  combustion  is  practically  instantaneous  and  rz=o. 

Formula  (104)  gives  this  maximum  value  for  v  because  it 
is  not  absolutely  correct,  but  only  approximate.  It  will  be 
remembered  that  in  its  deduction  it  was  stated  that  the 
value  for  v  was  expressed  in  the  form  of  a  series,  of  which 
the  first  two  terms  only  were  retained.  But  the  function 
represented  by  this  series  may  go  on  increasing  when  r 
decreases  below  the  value  which  makes  the  sum  of  the  first 
two  terms  a  maximum,  provided  the  sum  of  the  other  terms 
goes  on  increasing. 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  59 

The  value  of  r  corresponding  to  the  maximum  of  the 
first  two  terms  is  nevertheless  important,  because  it  marks 
the  limit  below  which  a  decrease  in  r  gives  only  a  slight 
increase  in  the  velocity.  It  is  not  advisable  to  pass  below 

this  value  of  t  in  practice,  because  a  =  f— J    enters  the 

pressure  formulas  (93)  and  (103)  to  the  second  power,  and 
r  being  in  the  denominator  of  the  value  of  a,  a  small  de- 
crease in  r  causes  a  rapid  increase  in  the  value  of  a,  and 
hence  in  that  of  the  maximum  pressure,  while  the  gain  in 
velocity,  as  shown  by  the  previous  discussion,  is  very  small. 

VALUE  OF  r  CORRESPONDING  TO  THE  MAXIMUM  VALUE 
OF  v. — The  particular  value  of  r  which  corresponds  to  this 
maximum  value  of  v  is  called  the  "  time  of  the  maximum." 

Differentiating  equation  (104)  with  respect  to  r,  placing 

-r-  —  o,  and  solving  for  r,  we  have,  calling  the  resulting 


value  rl9 


(I05> 


This  shows  that  for  a  given  form  of  grain,  the  value  of  rl 
or  the  time  of  the  maximum,  depends  on  the  calibre,  weight 
of  projectile,  and  length  of  travel,  and  is  independent  of  the 
charge  of  powder  and  density  of  loading. 

For  the  same  powder,  the  weight  of  the  projectile  p  is 
proportional  to  the  cube  of  the  calibre,  the  length  of  travel 
u  to  the  first  power  of  the  calibre,  and  hence,  since  $B\  is 
constant,  we  may  write,  from  (105), 


r  = 


(.06) 


or  the  time  of  the  maximum  is  proportional  to  the  calibre  of 
the  gun  ;  that  is,  to  obtain  the  greatest  velocity,  the  time  of 
burning  should  increase  as  tae  calibre  of  the  gun  increases, 
or  large-grain  powder  should  be  used  in  large  guns,  which 
proves  the  principle  enunciated  by  Rodman. 


60  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

30.  Modulus  of  Quickness— Value  of  Modulus— Velocity  and  Pres- 
sure as  Functions  of  this  Modulus. 

MODULUS  OF  QUICKNESS. — Powders  are  called  "quick" 
or  "  slow  "  depending  upon  their  action  in  a  given  gun.  A 
given  powder  may  be  "quick"  when  used  in  one  gun  and 
"  slow"  when  used  in  another.  For  example,  the  I.  K.  pow- 
der which  is  used  in  the  3.2o-inch  field-guns  is  "  quick  "  when 
used  in  the  8-inch  rifle,  and  "  slow  "  when  used  in  the  Spring- 
field rifle.  From  equation  (105)  we  can  calculate  the  value  of 
rl ,  or  the  time  of  the  maximum,  for  any  gun  and  powder. 

A  powder  whose  time  of  combustion  is  much  greater 
than  this  is  called  a  slow  powder  for  this  gun,  and  one  whose 
time  of  combustion  is  nearly  equal  to  this  is  called  a  quick 
powder  for  the  same  gun. 

Also  two  powders  fired  in  different  guns  are  considered 
equal,  as  regards  their  quickness,  if  their  times  of  combus- 
tion are  proportional  to  the  "  times  of  the  maximum"  of  the 
two  guns  considered.  Hence,  if  we  make 


(I07) 


and  call  this  ratio  x  the  "  modulus  of  quickness "  of  the 
powder,  we  can  say  that  the  quickness  of  a  powder  is  meas- 
ured by  its  modulus. 

On  this  basis  Sarrau  classifies  powders  as  follows : 

x  =  i.o,  very  quick  powder; 
x  =  0.9,  quick  powder  ; 
x '  =  0.8,  medium  powder  ; 
#•  =  0.7,  slow  powder  ; 
x  —  0.6,  very  slow  powder. 

VALUE  FOR  MODULUS,— We  have,  from  (107), 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  6l 

Substitute  for  r^  its  value  from  (105),  and  we  have 


and  since  from  (92) 

we  have 

x  —  $Bfi^- (108) 

VELOCITY  AS  A  FUNCTION  OF  THE  MODULUS  x.— To  ex- 
press the  velocity  as  a  function  of  the  modulus,  we  have 
for  the  subtractive  term  of  the  binomial  formula  (104)  from 
(1070), 


and  for  r  from  the  same  equation, 


xc 
Substituting  the  value  -  for  the  subtractive  term,  and  for  r 

I  fsi\  \ 

its  value  above,  in  the  factor  (^-J   in  the  binomial  formula, 
we  have 

Making 


we  have 


v  = 


62          TEXT-BOOK  OF  ORDNANCE  AND  GUNNERY. 

MAXIMUM  PRESSURE  AS  A  FUNCTION  OF  THE  MODULUS 
x.  —  By  a  similar  process  the  pressures  on  the  base  of  the  pro- 
jectile and  on  the  breech  may  be  expressed  in  terms  of  x. 

For  the  maximum  pressure  on  the  base  of  the  projectile 
we  have 


and  for  that  on  the  breech 


31.  Limit  of  Use  of  Binomial  Formula. 

It  has  been  shown  that  v  in  formula  (91)  becomes  a  max- 
imum when  t  decreases  to  a  particular  value  rt  ,  and  also 
that  v  should  not  be  a  maximum  for  this  particular  value  of 
r,  but  should  increase  continuously  as  -c  decreases. 

It  is  also  evident  from  (107)  that  when  r  becomes  rl  ,  x, 
the  modulus,  becomes  unity,  or  x  —  i.  That  is,  the  velocity 
is  a  maximum  by  formula  (91)  when  x  =  i. 

The  value  of  x  from  (108)  is 


("3) 


and  the  subtractive  term  of  the  binomial  formula  is 

.......    (,,4) 


which  is  \  of  x.  Hence  when  v  becomes  a  maximum  in  (91), 
x  becomes  unity,  and  the  subtractive  term  of  (91)  becomes  \. 
This  value  for  the  subtractive  term  would  then  mark 
the  limit  of  the  use  of  the  binomial  formula,  were  it  not  for 
the  fact  that  as  a  function  approaches  its  maximum  it 
changes  its  value  very  slowly,  and  hence  before  we  reach 
the  value  x  =  i,  the  binomial  formula  will  cease  to  give  cor- 
rect results.  For  this  reason  Sarrau  adopts  the  value  x  —  T»T 
for  the  particular  value  of  the  modulus  at  which  it  is  best  to 
cease  the  use  of  formula  (91). 


GUNPOWDER  AND    INTERIOR  BALLISTICS.  63 

When  x  =  T9T,  the  subtractive  term,  being  |  of  x,  will  be 
i  °f  TT  —  °-273-  Hence  we  have  for  determining  the  limit 
of  the  use  of  the  binomial  formula  the  rule :  Calculate  the 
value  of  the  subtractive  term  in  the  binomial  formula ;  if  it 
is  greater  than  0.273,  the  binomial  formula  is  not  applicable ; 
if  less  than  0.273,  it  is  applicable ;  or 

>  0.273,  do  not  use  binomial  formula ; 


<  0.273,  use  binomial  formula. 

32.  Monomial  Formula  for  Velocity. 

It  is  necessary,  from  what  precedes,  to  have  a  formula  for 
velocity  that  can  be  used  when  the  binomial  formula  ceases 
to  apply. 

It  is  deduced  as  follows  :  The  values  of  the  modulus  for 
all  powders  in  use  vary  between  narrow  limits  (0.6  to  i.o). 

Hence,  assuming  the  equation  (1090), 


A*)  = 

we  may  place 

........    (116) 


since  when  a  variable  changes  its  value  within  narrow 
limits,  the  function  is  proportional  to  some  power  of  the 
variable  properly  chosen.  It  is  necessary  now  to  find  the 
proper  value  of  n  in  (116). 

Differentiating  (116),  we  have 


r-//w  = 

L=;r/M    [See(n6).] 

Substituting  for  /(*)  and  fix)  their  values  from  (109*), 
we  have 

for  the  value  of  n  required. 


64  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Assume  equation  (no);  and  substitute  in  it  for  f(x)  its 
value  (116),  and  we  have 


Substitute  for  x  its  value  (107^),  and  make 


M  =-A($By-*N, (119), 


and  we  have 


Formula  (120)  is  a  general  form  of  the  binomial  formula 
(104),  and  will  give  the  same  values  for  v  as  the  binomial 
formula,  if  the  proper  values  for  n  be  substituted.  For  the 
particular  case  when  x  =  T9T  and  n  —  \  (120)  becomes 


This  equation  (121)  is  strictly  applicable  only  to  the  par- 
ticular case  for  which  it  was  deduced  ;  that  is,  for  x  =  T9T 
and  n  =  £;  but  by  examining  it  we  see  that  v  increases  con- 
tinuously as  t  decreases,  which  should  be  the  case,  while  in 
the  binomial  formula,  as  already  shown,  v  ceases  to  increase 
as  f  decreases. 

Hence  if  we  use  equation  (121)  for  all  values  of  x  equal 
to  or  greater  than  ^,  we  will  obtain  a  value  for  v  which  is 
correct  for  the  value  x  —  T9T,  and  for  all  values  of  x  greater 
than  T9T,  values  for  v  which  will  be  more  nearly  correct  than 
those  given  by  the  binomial  formula. 

This  is  called  the  "  monomial  formula"  for  velocity,  ana 
we  say  that  it  is  used  whenever  the  subtractive  term  in  the 


GUNPOWDER  AND    INTERIOR  BALLISTICS.  65 

binomial  formula  is  greater  than  0.273  ;  since  when  that  is 
the  case  the  binomial  formula  is  no  longer  applicable. 

When  the  subtractive  term  is  nearly  equal  100.273,  either 
formula  can  be  used. 

The  monomial  formula  is  usually  written 


(122) 


by  substituting  a  and  /?  for  their  values,  equation  (92). 

To  find  M,  Sarrau  assumes  a  type  powder  as  before, 
making  /  =  I,  T:  =  i,  and  thus  determines  a  and  ft.  The 
powder  is  then  fired  in  a  given  gun,  v  measured,  and  thus 
everything  is  known  in  (122)  except  M,  which  may  be  cal- 
culated. 

Its  value  thus  determined  is 

log  M  =  2.84571. 

33.  Calculation  of  the  Value  of  T. 

For  the  type  powder  t  —  i,  and  under  this  supposition 
the  values  of  A  and  B  are  deduced.  The  values  of  r  for  all 
other  powders  must  therefore  be  expressed  in  terms  of  the 
type  powder  as  unity.  That  is,  the  value  of  r  for  any  pow- 
der is  the  ratio  of  its  true  time  of  burning  to  that  of  the 
time  of  burning  of  the  type  powder. 

The  force  of  all  nitrate  powders  is  practically  constant, 
as  has  been  shown  ;  and  since  /=  i  for  the  type  powders,  it 
may  be  assumed  as  unity  for  all  powders  as  an  approximate 
value.  Making  /=  i  in  the  binomial  formula  (104),  we  have 


For  any  particular  powder  to  which  this  formula  is  ap- 
plicable, we  could  measure  v  and  determine  r,  since  all  the 
other  quantities  are  known,  if  the  equation  could  be  solved 
for  r.  But  it  is  found  that  this  solution  is  impossible. 


66  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

If  the  monomial  formula  applies  to  this  particular  pow 
der,  we  have,  making  /=  i, 


(125) 

In  (125),  placing 


we  have 

a*X* 


*  = 


and  this  may  be  easily  solved  and  the  value  of  r  obtained. 
For  any  powder,  however,  we  do  not  know  beforehand 
whether  the  binomial  or  the  monomial  formula  is  applicable, 
since  r  must  be  known  to  determine  this  point.  Again, 
while  the  value  of  f  is  very  nearly  unity  for  all  powders,  it 
is  not  exactly  unity  for  any  except  the  type  powder,  and 
hence  the  value  of  r  determined  as  above  by  the  monomial 
formula  would  not  be  correct. 

Under  these  circumstances  we  proceed  as  follows :  The 
value  of  r  determined  by  (127)  is  approximate,  but  the 
approximation  is  sufficiently  correct  to  show  which  formula 
is  to  be  used.  Substitute  the  value  of  r  from  (127)  in  the 
subtractive  term  of  the  binomial  formula 


=  B~T O2*) 

If  the  result  obtained  is  greater  than  0.273,  the  monomial 
iormula  applies  ;  if  less  than  0.273,  the  binomial. 

Then  calculate  a  by  the  pressure  formula  (103).  Substi- 
tute this  value  of  OL  in  either  the  monomial  or  the  binomial 
formula  according  as  the  former  or  the  latter  applies,  as  de- 
termined by  the  test,  and  solve  for  ft.  This  value  of  ft  sub- 
stituted in  the  formula 


GUNPOWDER   AND    INTERIOR  BALLISTICS.  67 

will  give  r.     The  value  of  r  thus  obtained,  substituted  in  the 
formula 


together  with  the  correct  values  of  a  and  a,  will  give/. 

34.  Determination  of  the  Characteristics  a  and  ft. 
ist  Method.  —  We  have,  equation  (92), 


Assuming  /=  i  for  all  powders,  we  can  calculate  a  and  A, 
for  any  service  form  of  grain  by  the  methods  already  ex- 
plained, and  illustrated  in  the  case  of  the  spherical  grain  ; 
r  can  be  calculated  by  the  method  explained  above,  in  terms 
of  the  type  powder  as  unity,  and  hence  we  find  a  and  ft. 

2d  Method.  —  In  the  second  method  we  find  the  values  of 
a  and  ft  directly,  without  determining  /,  a,  A,  and  r,  as 
follows  : 

The  characteristics  a  and  ft  enter  the  binomial  and  mono- 
mial formulas  (91)  and  (122),  and  a  enters  the  pressure  for- 
mula (103).  Hence,  for  a  given  piece,  powder,  and  projec- 
tile, if  we  measure  accurately  the  pressure,  and  substitute  it 
in  (103),  we  can  find  #,  and  substituting  the  measured  veloc- 
ity and  the  value  of  a,  just  found,  in  either  the  monomial  or 
the  binomial  formula,  whichever  is  applicable,  we  can  find  ft. 

$d  Method.  —  In  the  third  method  two  different  guns  are 
used,  and  the  velocities  accurately  measured  under  two  dif- 
ferent conditions  of  firing.  The  results  being  substituted  in 
the  binomial  formula,  or  in  the  monomial  and  binomial  for- 
mulas together,  will  give  two  equations,  containing  the  two 
unknown  quantities  a  and  ft,  from  which  they  may  be  ob- 
tained. 

The  following  table  gives  data  with  reference  to  Ameri- 
can guns  and  powders,  and  was  calculated  from  data  fur- 
nished from  the  Ordnance  Proving  Ground,  Sandy  Hook, 
N.J. 


68 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


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GUNPOWDER  AND   INTERIOR  BALLISTICS.  69 

35.  Effect  of  Variation  of  Elements  of  Loading  upon  Velocity,  and 

Maximum  Pressure. 
The  variable  elements  of  loading  for  any  gun  are  : 

1.  The  weight  of  the  charge  of  powder,  c3 

2.  The  density  of  loading,  A. 

3.  The  time  of  combustion  of  the  grain,  r. 

The  fixed  elements  are,  : 

1.  The  calibre,  c. 

2.  The  travel  of  the  projectile  in  the  bore,  u. 

3.  The  weight  of  the  projectile,/. 

For  the  same  force  of  the  powder  and  the  same  form  of 
grain,  having  c,  u,  and  p  constant,  we  may  vary  GO,  A,  and  r 
so  as  to  obtain  the  same  muzzle  velocity  with  a  different 
maximum  pressure  on  the  breech,  or  the  same  maximum 
pressure  with  a  different  muzzle  velocity.  In  this  discussion 
the  maximum  pressure  on  the  breech  is  alone  considered, 
since  it  is  always  greater  than  that  on  the  base  of  the  pro- 
jectile. There  are  an  infinite  number  of  sets  of  values  of 
c5,  J,  and  r  which  will  satisfy  these  conditions,  and  the  ques- 
tion is  to  determine  what  set  to  use. 

Assume  equations  (no)  and  (112),  and  regarding  c3,  J, 
and  r  as  variables,  take  the  Napierian  logarithms  of  both 
members  of  each,  differentiate,  and  we  have 


+fr;  ....  (I29) 

A        j(x 


+  • "30, 


Now 


Hence 


70  TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 

We  have  also,  from  (1160), 


Substituting  these  values  in  (129)  and  (130),  we  have 
dv       3  d&>       I  dA         dr 


dJ\_$d£       dA_       dr 
>    -^"  A"  t' 


These  equations  show  that  when  c3  and  A  increase,  v  and 
P9  increase,  and  when  r  increases,  v  and  P0  decrease  ;  and 
this  should  evidently  be  the  case. 

36.  Change  of  Velocity  when  Maximum  Pressure  remains  Con- 
stant —  Fixed  Powder-chamber. 

VARIATION  OF  VELOCITY.—  A  gun,  like  any  other  struc- 
ture, is  built  to  stand  a  certain  fixed  maximum  pressure,  and 
this  pressure  must  not  be  exceeded.  Therefore  the  most 
important  consideration  is  to  find  how  the  velocity  will 
vary  for  such  changes  in  c3,  A,  and  r  as  will  keep  the  maxi- 
mum pressure  constant  and  within  limits. 

To  do  this  we  will  consider  the  three  variables  GO,  A,  and 
t  in  order,  keeping  one  constant  and  varying  the  other  two, 
and  find  the  effect  upon  the  velocity,  the  pressure  being 
always  constant  and  a  maximum. 

I  st.  GO  constant,  A  and  r  variable.  —  Since  P0  and  c3  are 
constant,  we  have 


and  hence,  from  (133), 

dA      di 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  fl 

This  condition  must  hold  in  order  that  P0  be  constant. 
Substituting  the  above  value  of  --  in  (132),  we  have 

dv  dA 

--(t-«)T  .......    (134) 

The  value  of  n  is,  from  (117), 


2     3  —  x 

When  the  modulus  x  >  0.6,  which  corresponds  to  a  very 
slow  powder,  n  <  J,  and  hence  —  is  positive  and  increases 

with  A.  Therefore,  when  the  weight  of  the  charge  is  con- 
stant, we  see  from  (134)  that  we  may  increase  the  velocity 
by  increasing  the  density  of  loading  ;  but  in  order  to  keep 
the  pressure  constant,  (133^)  shows  that  we  must  use  a  slower 
powder. 

2d.  A  constant,  GO  and  t  variable.  —  P0  and  A  being  constant, 
we  have 

dP.  =  o  ; 


and  from  (133), 

3  doo       dr  , 

--  =     .........  <I34a> 


for  the  condition  that  P0  shall  be  constant. 

Substituting  this  value  of  -£-  in  (132),  we  have 


The  value  of  n  is 


(135) 

V  4  \2  I  GO 


?2  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

When  x  =  o,  n  —  \.  It  is  less  than  J  for  every  other 
value  of  x.  Hence  (£  —  ri)  is  always  positive,  and  -  -  in- 

creases with  c3. 

Therefore  when  the  density  of  loading  is  constant,  (135) 
shows  that  we  may  increase  the  velocity  by  increasing  the 
weight  of  charge,  but  (1340)  shows  that  in  order  to  keep  the 
pressure  constant  we  must  also  use  a  slower  powder. 

This  means  that  we  can  obtain  an  increase  of  velocity 
with  a  constant  maximum  pressure,  by  increasing  the  size 
of  the  chamber  and  using  a  larger  charge  of  slower 
powder,  and  this  is  the  general  method  employed  at  present. 

3d.  t  Constant,  do  and  A  Variable.  —  PQ  and  r  being  con- 
stant, we  have 

«//V-o; 

dr  =  o; 
and  from  (133), 

d&  dA 


for  the  condition  that  P0  shall  be  constant 

dA  . 
Substituting  this  value  of  —  r-  in  (132),  we  have 

dv  d™ 


Since  this  is  always  positive,  (136)  shows  that  for  the  same 
kind  of  powder  we  may  increase  the  velocity  by  increasing 
the  weight  of  charge,  but  (135^)  shows  that  in  order  to  keep 
the  pressure  constant  we  must  also  decrease  the  density  of 
loading. 

FIXED  POWDER-CHAMBER.—  In  the  preceding  discussion 
it  has  been  supposed  that  we  could  vary  the  size  of  the 
powder-chamber.  But  in  the  ordinary  case,  with  a  gun 
already  built,  the  powder-chamber  will  be  fixed  and  its 
volume  constant.  In  this  case  we  have 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  73 

Taking  the  Napierian  logarithms  of  both  members  and 
differentiating,  we  have 

dA      doo 

~A  '-''-& (137) 

Substituting  this  value  of  -j-  in  (132)  and  (133),  we  have 


dv        5  doo         dt 
^=8^~   -*7 

dPQ     _  7  d&       dr 
~        -~-'- 


039) 


The  variables  are  thus  reduced  to  two.  Now  if  we  sup- 
pose cS  and  t  to  vary  so  as  to  keep  P0  constant,  we  have 
dPa  —  o,  and  from  (139) 

dt       7  d(S 

7"   =  4  £-' 04°) 

for  the  condition  that  P0  shall  be  constant. 
Substituting  this  value  of  —  in  (138), 

dv 


When  x  =  0.6,  n  =  J  (see  1350) ;  and  for  larger  values  of 
x,  n  becomes  smaller ;  therefore  for  all  cases  in  practice  the 
second  member  of  (141)  is  positive,  and  v  increases  with  GO. 

Hence  (141)  shows  that  when  the  powder-chamber  is 
fixed,  we  may  increase  the  velocity  by  increasing  the  weight 
of  the  charge,  but  (140)  shows  that  in  order  to  keep  the 
pressure  constant  we  must  use  a  slower  powder.  That  is, 
we  use  a  larger  charge  of  slower  powder. 

37.  Relative  Variation  of  Velocity  and  Time  of  Combustion— Of 
Velocity  and  Maximum  Pressure — Limits  of  Modulus — Use- 
ful Practical  Formulas. 
VELOCITY  AND  TIME  OF  COMBUSTION.— To  determine 

the  relative  change  in  velocity  for  a  given  change  in  the 


74  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

time  of  combustion,  suppose  r  to  be  the  only  variable  in 
equation  (132).     Then 

dob  =  o  ;     d  A  =  o  ; 
and  the  equation  becomes 

dv              dr 
-SB  —  n — .     (142) 

v  t 

As  powder  becoms  slower  x  decreases.  But  as  x  de- 
creases n  increases  (see  1350).  In  fact,  n  may  be  called  the 
"modulus  of  slowness,"  since  it  increases  as  the  powder 
becomes  more  slow,  while  x,  or  the  "  modulus  of  quickness," 
increases  as  the  powder  becomes  quicker.  From  (142)  it  is 
evident  that  for  the  same  relative  change  in  the  time  of 
burning  the  effect  upon  the  velocity  will  be  greater  as  the 
powder  becomes  more  slow,  since  n  becomes  greater. 

This  is  one  of  the  principal  objections  to  using  very 
slow  powder,  because  small  irregularities  of  manufacture, 
which  are  always  apt  to  occur,  affect  r,  the  time  of  burning, 
and  cause  irregularities  in  velocity. 

VELOCITY  AND  MAXIMUM  PRESSURE. — In  the  same  way, 
to  determine  the  relative  change  of  velocity  and  maximum 
pressure,  suppose  t  the  only  variable  in  equation  (133). 

Then 

dob  =  o ;     dA  =  o ; 
and  the  equation  becomes 

Tr*'-~r 043) 


Substitute  this  value  of       in  (142)  and  we  have 

dv        dP, 

=»- (I44) 


From  this  we  see,  generally,  that  with  quick  powders, 
since  n  is  small,  a  given  increase  of  pressure  gives  only  a 


GUNPOWDER   AND    INTERIOR   BALLISTICS.  75 

very  small  increase  of  velocity,  and  for  slow  powders,  since 
n  is  large,  a  given  increase  of  pressure  gives  a  considerable 
increase  of  velocity.  Hence  it  is  advantageous  on  this 
account  to  use  slow  powders. 

LIMITS  OF  THE  MODULUS.  —  The  preceding  considera- 
tions may  be  applied  in  fixing  the  inferior  limit  of  the 
modulus  as  follows  : 

Equation  (144)  shows  that  as  x  decreases,  or  n  increases, 
a  given  increase  in  the  pressure  will  give  a  considerable 
increase  in  the  velocity,  and  hence  it  appears  to  be  advan- 
tageous to  use  a  slow  powder,  for  which  n  is  large.  But 
(142)  shows  that  for  large  values  of  n  we  have  great  irregu- 
larities in  v,  as  previously  explained,  and  Sarrau  has  fixed 
upon  0.6  as  the  value  of  x  below  which  it  is  not  expedient 
to  go  in  practice  in  order  to  avoid  these  irregularities. 

For  the  superior  limit,  when  x  —  T9T  or  n  =  £,  equation 
(144)  shows  that  the  relative  increase  of  velocity  is  only  one 
eighth  that  of  the  maximum  pressure  ;  and  since  the  mono- 
mial formula  was  deduced  for  this  value,  it  was  formerly 
regarded  as  the  superior  limit  of  the  modulus.  Other  con- 
siderations, however,  have  led  to  an  increase  of  this  value 
up  to  1.2  for  some  powders. 

USEFUL  PRACTICAL  FORMULAS.  —  In  practice  it  is  fre- 
quently required  to  find  what  change  in  velocity  and  press- 
ure a  given  change  in  weight  of  charge  will  produce  in  the 
same  gun.  For  this  purpose  assume  the  monomial  formula 
for  velocity 


For  any  other  charge  of  the  same  powder  whose  weight 
is  cS',  all  the  quantities  in  the  formula  will  remain  constant 
except  z/,  c3,  and  A.  The  value  of  A  is 


27.68c3 

A  =  - —  = 


76  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

K  being  a  constant.     Raising    both  members  to  the  one- 
fourth  power  and  multiplying  by  c3*, 


Dividing  the  value  of  v  by  that  of  z/,  we  have 
v       c3* 

t?  =  «e'i  ........  (I45) 

Similarly,  for  the  pressures  we  have 


Dividing  as  before,  we  have 

'  =       ........    046) 


These  formulas  are  correct  for  quick  powders  and  ap- 
proximately correct  for  slow  ones.  The  velocity  formula 
is  useful  where  it  is  necessary  to  find  the  charge  required 
to  give  a  certain  velocity  to  a  projectile  at  a  target  at  re- 
duced range,  as  in  armor-plate  experiments. 

38.  Pressure  Curves  in  Guns  —  Noble  and  Abel's  Method  —  Mayev- 
ski's  Method. 

It  is  necessary  in  designing  a  gun  to  know  the  pressures 
at  different  points  along  the  bore,  as  the  projectile  moves 
through  it,  under  the  action  of  the  powder-gas,  in  order  that 
the  gun  may  be  given  sufficient  strength  to  withstand  these 
pressures. 

The  accurate  solution  of  this  problem  is  attended  with 
great  difficulties,  and  can  hardly  yet  be  said  to  have  been 
successfully  accomplished.  Enough  is  known,  however,  to 


GUNPOWDER   AND    INTERIOR  BALLISTICS.  77 

furnish  safe  working  limits  in  designing  the  strength  of  the 
gun  at  different  points. 

NOBLE  AND   ABEL'S   METHOD.— They   assumed  an  ex- 
pression of  the  form 

(I47) 


in  which  x  is  the  distance  travelled  by  the  projectile,  t  the 

-+-H — i — * — 


irn n n 

-J          ' f 


FIG.  9. 

corresponding  time,  and  a,  a,  /3,  and  y  constants  to  be  deter- 
mined  by  experiment. 

Wires  were  inserted  into  a  gun  through  holes  drilled  at 
short  intervals,  as  shown  in  Fig.  9.  These  wires  carried 
currents  of  electricity,  which  were  broken  by  the  projectile 
in  its  passage  through  the  bore,  and  these  breaks  were  re- 
corded on  the  Noble  chronoscope,  which  is  an  instrument 
for  measuring  very  small  intervals  of  time. 

The  distance  between  the  holes  gave  x,  and  the  record 
of  the  chronoscope  /,  and  substituting  the  values  thus  ob- 
tained in  (147),  the  most  probable  values  of  the  constants 
were  determined  by  the  method  of  least  squares. 

Differentiating  (147)  with  respect  to  /  gives 


and  differentiating  this  with  respect  to  /  gives 

d*x       dv  /T  , 

W  =  Tt  ........    (I49 

the  acceleration. 

If   W  be  the  weight  of  the    projectile  and  P  the  total 
pressure  on  its  base,  we  have 


/  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

i 

MAYEVSKI'S  METHOD. — General  Mayevski  assumed 

x  =  At  +  £/*  +  a3  +  Dt*  +  etc.,  .     .     .     (151) 

and  by  experiment  determined  /,  having  x  given  by  the 
nature  of  the  experiments  (see  Fig.  10).  His  general  plan 
resembles  that  of  Noble  and  Abel,  but  differs  in  the  method 
of  conducting  the  experiments. 


FIG.  10. 


From  these  results  values  of  A,  B,  C,  and  D  were  deter- 
mined by  the  method  of  least  squares. 

Differentiating  (151)  with  respect  to  /,  we  have 


.,      .    (152) 


for  the  velocity  at  any  point. 
From  (152)  we  have 


(I53) 


for  the  acceleration  ;  and  for  the  point  where  this  is  a  maxi- 
mum we  have,  from  (153), 


— 


(154) 


39.  Longridge's  Method. 

Mr.  Longridge,  an  English  engineer,  uses  a  combination 
of  Noble  arid  Abel's  and  of  Sarrau's  formulas  as  follows  : 

Noble  and  Abel's  formula  for  the  pressure  curve  is,  see 
(45), 


GUNPOWDER   AND    INTERIOR  BALLISTICS.  79 

in  which  p  is  the  pressure  corresponding  to  the  volume 
z/',  v'  is  the  volume  of  the  powder-chamber  supposed  to  be 
entirely  filled  with  powder,  and  v"  any  other  volume  of  ex- 
pansion. 


E 


Let  AB,  Fig1.  11,  represent  the  reduced  length  of  the 
powder-chamber,  that  is,  the  length  of  a  cylinder  whose 
diameter  is  that  of  the  bore  and  whose  volume  is  that  of 
the  powder-chamber. 

Suppose,  according  to  Noble  and  Abel's  hypothesis,  that 
all  the  powder  is  burned  before  the  projectile  moves  from 
its  position  B.  Make  v"  —  v'  in  (155),  and  we  have/  —  43 
tons. 

This  is  the  pressure  that  would  exist  in  the  chamber  if 
the  powder  were  all  burned  before  the  projectile  moved. 

Lay  off  BB'  =  43  tons.  Assume  different  values  for  v" ', 
corresponding  to  C,  D,  E,  etc.  Calculate  the  corresponding 
ordinates  from  (155),  and  erect  them  at  the  corresponding 
points. 

The  resulting  curve  B'C'D'E'  will  be  Noble  and  Abel's 
pressure  curve. 

Now  it  is  known  that  the  powder  is  not  all  burned  before 


8O  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

the  projectile  moves,  and  hence  the  pressure  BB'  —  43  tons 
cannot  exist  in  a  gun. 

The  maximum  pressure  that  does  exist  is  given  by  Sar- 
rau's  formula  for  the  maximum  pressure  on  the  breech. 

P0  =  A>M/£V. 

Calculate  this  pressure,  lay  off  A  A'  at  the  breech  equal 
to  it,  and  assume  this  pressure  to  be  uniform  from  the  breech 
to  the  point  of  maximum  pressure  in  the  bore.  Substitute 
this  value  of  P0  for  p  in  (155)  and  find  the  corresponding 
value  of  v" .  This  value  of  v"  will  give  the  point  P  in  the 
bore  at  which  the  maximum  pressure  occurs.  The  line  A'P'' 
will  be  parallel  to  AP,  and  the  curve  of  pressures  will  be 
A'P'C'D'E'. 

Let  ^,  —  AB,  the  reduced  length  of  the  powder-chamber; 
x  =  any  other  length  measured  from  A.  Then 


and  equation  (155)  becomes 

(       43       )  '-074 


which  is  more  convenient  for  use. 

The  pressure  at  B  is  originally  zero  and  rises  to  a  maxiv 
mum  at  P'.  Hence  the  actual  pressure  curve  has  the  form 
BP'C'D'E'. 

The  form  of  the  curve  from  B  to  Pr  is  not  important,  as 
its  maximum  ordinate  only  is  required. 

40.  Pressure  Curve  by  Sarrau's  Formulas. 

The  pressure  curve  in  a  gun  may  also  be  obtained  from 
Sarrau's  velocity  formulas,  as  follows: 

For  a  slow  powder  we  have 


v  = 


GUNPOWDER   AND    INTERIOR  BALLISTICS.  8  1 

In  (1560)  u  is  expressed  in  inches.  In  (161),  following,  v 
and  g  are  in  feet,  and  u  must  be  expressed  in  feet  in  order 
that,  when  du  is  substituted  in  (161),  all  the  quantities  may 
have  the  same  unit. 

Hence  in  (156^)  we  write 

u*  inches  =  I2V  feet; 

and  in  the  subtractive  term 

( 

«*  inches  =  I2*«*  feet. 
Place 

v  =  au\i  -  6u*)9  .......    (157) 

in  which  u  is  in  feet,  and 


X  12* 


From  mechanics  we  have 


du  =  vdt\      .'.  dt  =  — . 


Substituting  in  the  value  of  Pf,  we  have 


059) 


g 


82  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

p  being  the  weight  of  the  projectile,  and  ;//  it's  mass  ;  and  if  GO 
denote  the  area  of  the  base  of  the  projectile  in  square  inches, 
we  have  for  the  pressure  in  tons  per  square  inch  on  its  base, 


.    du t'6') 

Differentiating  (157),  we  have 

^v  —  3      -*      7 

du  ~  8 a'        ~  8  a  H    ' 

and 

vdv      357 

^7=8'Z"":   -  4*'*"1  +  g«V*».     •     •     •     (162) 

Hence 

P'7  =  /          _  f~3^  9  _d  _  5_  , ,  j   ,   7 ;  ,  ,8  t~|       6 

2240X<»X^L8^  4^         '8^        J*    ( 

For  quick  powders  we  have 


71  — 


*     -' 

which  may  be  placed  in  the  form 

v  =  a'w\     .........     (164) 

u  being  in  feet  as  before  explained,  and 

,       Ma/3-*&4Vx  12* 

-ph  ~  ..... 

Differentiating  (164),  we  have 


GUNPOWDER   AND    INTERIOR   BALLISTICS.  83 

and 

vdv       3 

~du  =  i6a  *•'•      ......     ('6;) 

Hence 


Since  these  curves  are  obtained  on  the  adiabatic  hypothe- 
sis, they  may  be  considered  as  marking  the  interior  limit  of 
pressures,  and  the  true  pressure  curve  probably  lies  between 
the  latter  and  those  obtained  by  Longridge's  method. 

It  must  be  remembered  that  the  pressures  given  by  these 
equations  (163)  and  (168)  are  those  producing  motion  of  the 
projectile,  and  do  not  represent  the  total  pressure  on  the 
base. 

41.  Determination  of  Velocity  by  Experiment—  General  Principles 
—Targets  for  Cannon—  For  Small  Arms. 

In  order  to  verify  the  formulas  for  velocity  and  pressure 
previously  deduced,  it  is  necessary  to  determine  accurately 
by  experiment  the  velocity  of  the  projectile,  and  the  pressure 
in  the  gun,  clue  to  a  given  charge  of  powder,  under  given 
conditions  of  loading. 

VELOCITY.  —  The  velocity  of  a  projectile  is  determined  by 
measuring  the  time  of  its  passage  over  a  given  distance. 

Let  A  and  B  be  two  points  whose  distance  apart  is  s,  and 
t  the  time  of  passage  of  the  projectile  over  this  distance. 
Then,  since 

s 
v  =  -, 

v  will  be  the  mean  velocity  of  the  projectile  over  the  dis- 
tance s,  or  its  velocity  at  the  middle  point  between  A  and  B. 
In  order  that  this  may  be  true,  the  space  s  must  be  so  small 
that  the  motion  of  the  projectile  may  be  considered  uniform 
and  in  a  right  line.  As  neither  of  these  conditions  holds  in 
practice,  v  will  not  be  the  velocity  at  the  middle  point  be- 
tween A  and  B,  but  it  will  be  sufficiently  correct  for  all 
practical  purposes  to  assume  that  it  is. 


84  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

GENERAL  PRINCIPLES.  —  In  order  that  we  may  know  ex- 
actly the  time  of  passage  of  the  projectile  over  the  distance 
s,  we  must  have  first  an  accurate  scale  of  time,  and  second, 
we  must  mark  on  this  scale  the  instant  that  the  projectile 
passes  the  two  points  A  and  B.  The  difference  between  the 
times  of  passage  of  the  points  A  and  B  will  then  give  the 
time  of  passage  over  the  distance  s,  and  knowing  this  time 
we  can  find  the  mean  velocity.  The  passage  of  the  projec- 
tile over  the  points  A  and  B  is  marked  on  the  time-scale  as 
follows  : 

Two  targets  are  set  up,  one  at  A  and  the  other  at  B. 
Electric  currents  circulate  through  these  targets,  and 
also  through  the  instrument  which  furnishes  the  scale  of 
time. 

When  the  projectile  passes  the  target  at  A  it  breaks  the 
circuit,  and  this  break  is  registered  by  the  instrument. 
When  it  passes  B  the  same  thing  occurs.  The  differ- 
ence between  these  breaks  measured  on  the  scale  of 
time,  and  corrected  for  errors,  gives  the  time  of  passage 
required. 

TARGETS  FOR  CANNON.  —  The  functions  of  the  targets  are 
then  to  mark  the  points  in  the  path  of  the  projectile  between 
which  its  velocity  is  to  be  measured,  and  to  support  the 
wires  carrying  the  electric  currents  which  are  to  be  broken 
by  the  passage  of  the  projectile.  For  cannon,  the  first  target 
is  placed  at  such  a  distance  from  the  muzzle  that  it  will  not 
be  injured  by  the  blast.  Call  this  distance  xiy  and  the  dis- 
tance from  the  muzzle  to  the  middle  point  between  the  tar- 
gets x  ;  then 


The  velocity  found  by  experiment  is  at  the  point  —  ;  that 

which  we  wish  to  find  is  at  the  muzzle,  or  the  initial  velocity. 
By  formulas  in  "  Exterior  Ballistics  "  we  can  find  the  latter, 
when  the  former,  at  the  distance  xi  is  known. 

Each  target  for  cannon  generally  consists  of  a  frame  of 
wood  carrying  a  number  of  small  parallel  copper  wires. 


GUNPOWDER  AND   INTERIOR  BALLISTICS. 


FIG.  12. 


The  wires  are  so  arranged  that  the  current  entering  one 
side  of  the  target  must  traverse  all  of  them  before 
passing  out  at  the  other  side,  so  that  the  breaking 
of  any  wire  will  break  the  current.  The  wires  are 
drawn  as  tight  as  possible  in  order  that  the  break 
may  be  abrupt,  and  the  distance  between  them 
depends  on  the  diameter  of  the  projectile,  as  it 
must  be  impossible  for  it  to  pass  through  with- 
out breaking  at  least  one  wire.  The  breaks  are 
repaired  after  each  fire. 

The  target  is  shown  in  Fig.  12. 

SMALL-ARM  TARGETS. — As  there  is  practically  no  blast 

with  small  arms,  the  first  target  is  placed  at  the  muzzle,  and 

consists  of  a  single  wire  drawn  tightly  across  it.     To  avoid 

repairing  the  second  target,  it  consists  of  a  steel  plate  to  stop 

the  bullets.  On  its  rear  face  is 
secured  a  spring  insulated  from 
the  plate  (Fig.  13).  This  spring, 
s,  is  fixed  at  one  end  to  an  insu- 
lating substance,  such  as  a  block 
of  wood,  wy  and  the  other  end 

rests  on  a  metallic  pin,/.  The  current  passes  through  the 
spring  and  pin.  When  the  bullet  strikes  the  steel  plate,  the 
shock  causes  the  spring  to  leave  the  pin,  and  thus  the  current 
is  broken.  The  elasticity  of  the  spring  causes  it  instantly  to 
resume  its  former  contact  with  the  pin,  and  thus  renders  any 
repairs  unnecessary. 

42.  The  Ballistic  Instruments— Description  of  the  Le  Bouleng6 
Chronograph. 

The  functions  of  the  ballistic  instruments  are  to  furnish 
an  accurate  scale  of  time,  and  to  record  on  that  scale  the 
rupture  of  the  targets  by  the  passage  of  the  projectile. 

LE  BOULENGE  CHRONOGRAPH.— The  instrument  gener- 
ally used  for  this  purpose  was  invented  by  Captain  Le 
Boulenge  of  the  Belgian  Artillery,  and  is  called  the  Le  Bou- 

lenge  Chronograph. 

Scale  of  Time  —Its  scale  of  time  is  furnished  as  follows : 
Two    rods   are   suspended   vertically   from  electro-mag-' 


86 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


nets,  and  the  currents  which  pass  through  the  magnets, 
pass  also  through  the  targets.  Each  electro-magnet  has  its 
own  current  and  its  own  target,  and  is  independent  of  the 
other. 

When  the  first  target  is  broken,  one  of  the  magnets  is 
demagnetized  and  its  rod  falls.  When  the  second  target  is 
broken,  its  magnet  is  demagnetized  and  its  rod  falls.  The  fall 
of  this  second  rod  makes  a  mark  on  the  first  rod  while  it  is 
falling,  and  the  distance  h'  from  the  origin  of  fall  to  this 
mark  is  measured.  Then  we  have,  from  the  laws  of  falling 
bodies, 


which  furnishes  the  scale  of  time. 

Record  of  Breaking  of  Target 
—  Description  of  Instrument.— 
The  method  of  making  the 
record  will  appear  from  a  de 
scription  of  the  instrument,  Fig. 
14. 

Its  principal  parts  are  a  ver- 
tical column  of  brass,  B,  which 
is  supported  by  a  triangular 
bed-plate,  C,  and  this  bed-plate 
rests  upon  a  support  or  stand, 
5.  To  the  brass  column  are 
attached  two  electro  -magnets, 
EE ' .  The  magnet  E  supports 
the  long  rod  a  of  the  instru- 
ment, called  the  chronometer. 
This  rod  when  in  use  is  en- 
veloped by  a  zinc  or  copper 
tube,  z,  called  the  recorder, 
upon  which  the  mark  is  made. 
The  magnet  E'  supports  the 
short  rod  b,  called  the 
trar. 


regis- 
FIG.   14. 

Fig.  15  shows  the  details  of  the  marker,  or  part  of  the. 


GUNPOWDER  AND    INTERIOR   BALLISTICS, 


instrument  which  makes  the  record  of  the  breaking  of  the 
target.  It  consists  of  a  cir- 
cular knife,  m,  on  the  end  of 
a  spring,  s,  which  causes  it 
to  move  to  the  right  in  the 
figure.  The  trigger,  /,  is 
supported  in  its  fulcrum  on 
the  bed-plate.  Its  right  end 
terminates  in  a  catch,  which 
engages  in  a  corresponding 
one  on  the  knife,  and  pre- 
vents the  latter  from  moving 
to  the  right,  under  the  action 
of  the  spring,  till  the  catch  is 
freed.  The  left  end  of  the 
lever  is  acted  on  by  a  spring 
s',  which  presses  it  upwards, 
and  keeps  the  catch  engaged 
with  the  knife.  The  piece  marked  b  is  a  disk  which  screws 
into  the  left-hand  end  of  the  lever,  and  which  may  be  raised 
or  lowered  by  means  of  the  screw. 

Above  the  disk  is  a  tube  or  cup  which  retains  the  short 
rod  b  after  its  fall.  The  record  is  made  by  the  short  rod 
falling  on  the  disk  b,  depressing  it,  and  releasing  the  knife 
;;/  from  the  catch  on  the  trigger.  The  knife  then  moves  to 
the  right  and,  striking  the  long  rod  in  its  fall,  makes  the 
required  record. 

43.  Arrangement  of  Wires — Working  of  Instrument — Disjunction. 

ARRANGEMENT  OF  WIRES. — The  arrangement  of  the 
wires  depends  upon  whether  the  time  to  be  measured  is 
comparatively  great  or  small.  When  great,  the  wires  are 
arranged  as  follows,  Fig.  16. 

The  chronometer  is  supported  by  the  upper  magnet.  The 
first  current  comes  from  the  battery  to  the  upper  magnet, 
E\  from  the  magnet  E  to  the  disjunctor,  whose  functions 
will  be  explained  later ;  from  the  disjunctor  to  the  first  target, 
and  from  the  first  target  to  the  battery.  The  course  of  the 
second  current  is  similar  and  can  be  readily  followed. 


88 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


The  instrument  thus  arranged  i-s  called  a  megagraph. 
WORKING. — When  the  first  target  is  broken,  the  chronom- 
eter falls ;  when  the  second  target  is  broken,  the  registrar 


FIG.  16. 

falls,  and,  striking  the  disk  of  the  trigger,  makes  the  record 
on  the  chronometer,  as  at  R,  Fig.  14. 

The  point  on  the  chronometer  from  which  all  heights 
are  measured  is  the  mark  O,  Fig.  14,  made  on  this  rod  by 
the  knife  when  the  chronometer  is  susperided  by  its  magnet. 
Denoting  the  height  OR  by  ti ,  the  corresponding  time  is 


and  is  the  time  which  elapses  from  the  fall  of  the  chronom- 
eter till  the  record  is  made.  It  is  not,  however,  the  time  of 
passage  of  the  projectile  between  the  targets,  because— 

1.  There  is  a  certain  time  required  for  the  demagnetiza- 
tion of  the  magnet  E.     Hence  the  chronometer  does  not  fall 
at  the  instant  the  first  target  is  broken,  and  the  time  is  too 
short  by  this  amount,  which  we  call  /,. 

Instead  of  making  the  record    the   instant  the   second 
target  is  broken,  there  is  a  delay  caused  by— 

2.  The  time  required  to  demagnetize  E'  =  /,. 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  89 

3.  The  time  required  for  the  registrar  to  fall  to  the  disk 
of  the  trigger  =  /,. 

4.  The  time  necessary  to  disengage  the  trigger,  and  for 
the  knife  to  move  forward  and  make  the  record  on  the  chro- 
nometer =  /4. 

During  these  last  three  intervals  the  long  rod  is  falling, 
and  hence  the  height  of  fall,  and  consequently  the  time,  is 
too  great  by  their  sum.  Hence  the  true  time  is 


and  to  find  the  true  value  of  t  it  is  necessary  to  find  the 
values  of  these  times,  since  T  is  known. 

To  do  this  it  is  not  necessary  to  find  the  value  of  each 
single  interval,  since  the  total  time  can  be  readily  obtained. 
If  we  break  both  currents  at  the  same  instant,  it  is  evident 
that  all  the  delays  mentioned  will  still  exist.  The  delay  in 
falling  of  the  chronometer,  and  that  of  making  the  record 
by  the  registrar,  will  be  marked  on  the  long  rod  as  it  falls, 
and  will  be  found  at  a  certain  height  above  O,  as  at  D,  Fig.  14. 
This  height  is  called  "  the  disjunction,"  and  the  time  corre- 
sponding to  this  height  is  the  algebraic  sum  of  all  the  times 
before  named. 

Let 

*  =  (',  +  ',  +  O-'r 
Then 


in  which  h  is  the  height  OD.     Hence 

r_0_A/^          /?* 
V     g        \j  g' 

It  must  be  remembered  that  difference  of  times  and  not 
difference  of  heights  is  to  be  taken. 

FIXED  DISJUNCTION.— For  the  velocity  at  the  middle 
point  between  targets  we  have 


90  TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 

Substituting  for  t  its  value,  we  have 


v  = 


g 

From  this  equation  we  see  that  if  the  values  of  s,  and  of 

—  or  the  disjunction,  be  fixed,  the  values  of  v  can  be 
g 

calculated    and  tabulated    for  all  values  of    h'  within  the 
limits   of   practice.      This   has   been   done   for   the    values 

s=  100  feet  and  \/ —  =  0.15    second,  and    this  value  of 


2h 

\     --  =  o- 

V  g 


—  is  called  the  fixed  disjunction.     If  the  above  table  is 
g 

not  at  hand,  this  fixed  value  of  the  disjunction  avoids  the 
labor  of  calculating  6  or  \     --  for  each  shot. 
Hence  in  this  case 

/=  T  —  0.15  sec.  =  A  /—  —0.15. 

V  s 

To  fix  the  disjunction,  the  disk  b  on  the  trigger  /  may 
be  raised  or  lowered  to  regulate  the  height  of  fall  of  the 
registrar  till  B  =  o.  1 5  sec. 

44.  Arrangement  of  Wires  for  Small  Times— Disjunctor— Measur- 
ing-rule. 

ARRANGEMENT  OF  WIRES. — Under  ordinary  conditions, 
the  distance  between  targets  is  so  great,  that  the  chronometer 
acquires  considerable  velocity  in  falling,  before  the  record 
is  made  by  the  registrar.  As  the  distance  between  targets 
decreases  there  will  be  less  interval  between  the  breaking 
of  the  two  currents,  and  consequently  between  the  fall  of  the 
two  rods.  Hence  the  record  will  be  made  before  the  chro- 
nometer has  acquired  much  velocity,  and  small  differences 


GUNPOWDER   AND    INTERIOR   BALLISTICS. 


in  reading  will  correspond  to  considerable  differences  in 
time.  A  small  error  in  reading,  therefore,  will  correspond 
to  a  large  error  in  time.  As  the  distance  between  targets 
decreases,  the  record  will  approach  the  disjunction  circle, 
and  will  fall  on  that  circle  when  the  distance  is  zero,  or 
when  both  currents  are  broken  simultaneously.  To  measure 
these  short  intervals  of  time  accurately  it  is  necessary  to 
allow  the  chronometer  to  acquire  considerable  velocity 
before  the  record  is  made  upon  it. 

This  necessitates  a  new  arrangement  of  wires  and  mag- 
nets, as  in  Fig.  17.  The  magnet  which  supports  the  regis- 
trar is  changed  from  below  to 
above  that  which  supports  the 
chronometer,  and  the  first  cur- 
rent runs  from  the  battery  to 
the  registrar  magnet,  thence 
to  the  disjunctor  and  to  the 
first  target,  so  that  the  regis- 
trar will  fall  first.  With  this 
arrangement,  if  both  currents 
be  broken  simultaneously,  the 
"  disjunction "  will  be  made 
near  the  top  of  the  chronom- 
eter at  D,  when  its  velocity  is 
greatest.  When  the  registrar 
falls  first,  as  it  does  in  actual 
use  in  determining  velocity,  it 
is  evident  that  the  record  will 
be  made  at  some  point  be- 
low the  disjunction,  as  at  R. 
The  same  method  is  followed 
in  determining  the  time  as  be- 
fore, except  that  the  time  cor-  S~^ 
responding  to  the  record  must" 
be  subtracted  from  that  corre- 
sponding to  the  disjunction,  for  the  time  of  passage  between 
targets.  The  instrument  thus  arranged  is  called  a  mi< 

.—This  instrument  is  used  for  breaking  both 


R 


0 


FIG.  17. 


92  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

currents   simultaneously  in   order  to    determine   the  alge- 
braic sum  of  all  the  times  /,,  t^,  /,,  etc. 

It  consists  (Fig.  18)  of  two  steel  blades,  nri ,  mounted  on 


FIG.  18. 

a  block  of  wood.  These  blades  are  attached  at  one  end, 
m  m' ,  to  the  block,  and  carry  binding-screws  at  this  end.  At 
the  other  end  they  rest  on  two  brass  pins,  b  b' ,  and  these 
pins  are  connected  with  the  binding-screws  shown.  Be- 
tween these  blades  is  a  strong  spring,  r,  with  a  knob,  s,  and  a 
spring-catch,  g.  At  right  angles  to,  and  attached  to  this 
spring  r  is  a  cross-piece,  pq.  The  action  is  as  follows  : 

When  the  spring  r  is  pressed  down  by  pushing  on  the 
knob  s,  it  is  caught  and  held  under  the  spring-catch  g,  and 
the  cross-piece  is  not  in  contact  with  the  blades  n  nf. 

Under  these  circumstances  the  blades  rest  on  their  pins 
b  b' ,  and  the  current  from  each  battery  enters  its  own  blade 
by  the  binding-screws  and  posts,  and  passes  to  its  target. 

But  when  the  trigger  or  catch  g  is  pulled  back  quickly, 
the  spring  r  is  released,  and,  rising,  its  cross-piece/^  strikes 
both  blades  n  n'  at  the  same  instant,  lifts  them  from  the  pins 
b  b',  and  breaks  both  circuits. 

MEASURING-RULE.  —  To  facilitate  measurements,  the 
heights  corresponding  to  all  velocities  within  the  ordinary 
limits  of  experiment  are  inscribed  on  a  metal  rule  furnished 
with  a  sliding  index.  The  heights  are  in  millimetres,  and 
must  be  reduced  to  feet  for  use  with  English  measures.  A 
table  of  times  corresponding  to  heights  in  millimetres  has 
been  calculated,  and  by  its  use  the  above  reduction  may  be 
avoided.  The  sliding  index  has  a  knife-edge  attached  to  it, 
and,  to  obtain  the  reading,  this  knife-edge  is  placed  on  the 
mark  made  by  the  marker  on  the  chronometer,  a  pin  on  the 
lower  part  of  the  scale  having  been  inserted  in  a  hole  in  the 


GUNPOWDER   AND    INTERIOR  BALLISTICS.  93 

chronometer  at  the  lower  end  to  bring  the  zero  point  of  the 
scale  opposite  the  origin  of  fall.  The  height  can  then  be 
read  off. 


45.  Adjustments— Use— Objections  to  the  Instrument— Br6ger's  Im- 
provements. 

ADJUSTMENTS. —  The  instrument  must  be  properly 
mounted  on  a  stand  at  such  a  distance  from  the  gun  that  it 
will  not  be  affected  by  the  shock  of  discharge,  and  connected 
with  the  batteries  and  targets,  and  be  then  adjusted  for  use. 

The  adjustments  are  three  : 

1.  Levelling. — The  object  of  this  adjustment  is  to  make 
the  bed  of  the  instrument  level,  and  consequently  the  brass 
column  or  standard  vertical.*-  The  chronometer  is  used  for 
this  purpose.     The  enveloping  tube  or  recorder  is  first  put 
on,  and  when  in  place  must  rest  closely  against  the   bob. 
Having  cocked  the  knife,  suspend  the   chronometer   and 
recorder  from   its  magnet,  and  move  the  levelling-screws 
which  pass  through  the  bed-plate,  till  the  bob  of  the  chro- 
nometer rests  in  a  square  notch  in  the  bed-plate.     The  stand- 
ard is  now  vertical, 

2.  Regulating  the  Magnets.— To  regulate  the  strength  of 
the  magnets,  each   of  the  rods  is  -provided  with  a  weight 
which  is  one  tenth  that  of  its  rod.    Place  the  proper  weight 
on  the  chronometer,  and  suspend  it  with  this  weight  from  its 
magnet,  the  core  of  which  is  movable,  and  draw  out  this 
core   till   the    rod    and  weight   fall.     The   strength   of  the 
magnet  is  by  this  means  regulated.     Do  the  same  for  the 
short  rod,  or  registrar,  and  its  magnet. 

3.  Fixing  the  Disjunction  Reading.— For  the   megagraph 
this   reading   is   at   a   fixed    height,  corresponding  to  0.15 
second.     To  make  the  adjustment,  place  the  sliding  index 
on  the  rule  at  the  mark  "  disjunction,"  and  clamp  it. 

Place  the  pin  of  the  rule  in  the  hole  in  the  bob  of  the 
chronometer,  bring  the  knife-edge  of  the  rule  to  bear  against 
the  copper  tube  on  the  chronometer,  and  turn  this  tube 
around  the  chronometer.  The  knife-edge  will  describe  a 
circle  on  this  tube,  called  the  "  disjunction  circle,"  and  the 
disjunction  reading  must  fall  on  this  circle.  To  test  it, 


94  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

suspend  both  rods  from  their  magnets,  and  break  both  cur- 
rents by  means  of  the  disjunctor.  If  the  mark  made  by  the 
knife  falls  on  the  circle,  no  adjustment  is  necessary ;  if 
above  the  circle,  the  fall  of  the  registrar  is  too  great ;  and 
if  below,  the  fail  is  too  small.  The  height  of  fall  of  the 
registrar  is  diminished  or  increased  by  raising  or  lowering 
the  disk  on  the  left-hand  end  of  the  trigger  /.  The  instru- 
ment is  now  ready  for  use. 

USE. — In  using  it,  first  cock  the  knife  or  marker,  suspend 
the  long  and  short  rods,  and  take  a  disjunction  reading.  If 
the  disjunction  is  not  exact,  correct  as  above.  If  exact, 
cock  the  knife  again,  suspend  the  rods,  fire  the  piece,  and 
read  the  height  with  the  rule.  Find  the  time  corresponding 
to  this  reading,  subtract  from  it  the  time  corresponding  to 
the  disjunction,  which  is  0.15  second  when  the  instrument 
is  used  as  a  megagraph  ;  or  if  used  as  a  micrograph,  sub- 
tract the  time  corresponding  to  this  height  from  that  corre- 
sponding to  the  disjunction,  as  previously  determined,  and 
the  remainder  will  give  the  time  of  passage  of  the  projectile 
between  targets.  Divide  the  distance  between  the  targets 
in  feet  by  this  time  in  seconds,  and  the  quotient  will  be  the 
velocity  of  the  projectile  at  a  point  midway  between  the 
targets. 

OBJECTIONS  TO  THE  INSTRUMENT. — The  principal  source 
of  error  in  the  Le  Boulenge  arises  from  the  fact  that  the 
circuits  are  not  broken  similarly  by  the  disjunctor  and  by 
the  projectile. 

When  the  circuits  are  broken  by  the  projectile,  the  re- 
tardation of  demagnetization  is  modified,  and  unequally  so 
for  the  two  magnets,  because  they  sustain  different  weights 
and  are  consequently  of  different  strength. 

BREGER'S  IMPROVEMENTS. — This  has  led  to  modifications 
of  the  instrument  by  Captain  Breger  (Fig.  19).  The  princi- 
pal of  these  are,  the  two  rods  are  made  of  exactly  the  same 
weight,  and  consequently  the  electro-magnets  are  of  the 
same  strength.  Their  axes  are  vertical  instead  of  horizon- 
tal. The  parts  generally  are  heavier  and  more  firmly  sup- 
ported. 

The  height  of  fall  of  the  registrar  is  regulated  by  raising 


GUNPOWDER   AND    INTERIOR   BALLISTICS. 


95 


or  lowering  its  magnet,  £',  and  the  disk  of  the  trigger  on 
which  the  registrar  strikes  is  fixed 
with  reference  to  the  lever.  The 
knife  is  square  instead  of  circular. 
The  disjunctor  has  been  modified 
so  as  to  insure  the  simultaneous 
rupture  of  the  two  circuits,  and 
the  strength  of  the  currents  is  reg- 
ulated by  resistance-coils.  These 
improvements  render  the  instru- 
ment much  more  accurate  than 
the  old  form. 


E 


E' 


FIG.  19. 


46.  Schultz  Chronoscope  —  Marcel- 
Deprez  Registers— Bashforth  Tar- 
gets. 

SCHULTZ  CHRONOSCOPE.— The 
Le  Boulenge  Chronograph  meas- 
ures velocity  at  one  point  only. 
If  the  velocity  of  a  projectile  is  to 
be  measured  at  several  points,  a 
separate  instrument  is  required  for 
each  point,  and  this  arrangement 
would  be  troublesome,  besides  hav- 
ing other  objections. 

It  is  frequently  necessary  to 
measure  the  velocity  of  the  same  projectile  at  different 
points,  as  in  determining  the  laws  of  the  resistance  of  the 
air  to  its  motion,  and  also  it  is  sometimes  required  to  deter- 
mine its  velocity  at  different  points  in  the  bore.  For  such 
purposes  an  instrument  must  be  used  which  will  give  a 
scale  of  time  of  such  an  extent  that  all  the  phenomena  may 
be  registered  upon  it. 

There  are  several  instruments  of  this  class,  and  as  a  type 
of  them  the  Schultz  chronoscope,  one  of  the  best  known, 
will  be  briefly  described  (Fig.  20). 

Scale  of  Time.— In  this  instrument  a  cylinder  a  revolves 
by  means  of  clockwork,  and  this  cylinder  has  also,  in  the 
older  form  of  machines,  a  motion  of  translation  parallel  to 


96 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


its  axis.  In  the  most  recent  form  the  cylinder  rotates  only, 
while  the  point  b,  which  describes  the  scale,  has  the  motion 
of  translation. 

The  point  b  is  a  quill  attached  to  one  branch  of  a  tuning-, 
fork,  c.  This  point  may  be  made  to  rest  lightly  against  the 
surface  of  the  cylinder,  or  may  be  withdrawn  from  contact 
with  it.  On  each  side  of  the  tuning-fork  is  an  electro- 
magnet, d. 

The  object  of  the  magnets  is  to  start  the  fork  vibrating, 
to  keep  up  this  vibration  during  the  experiment,  and  to 


FIG.  20. 

equalize  the  amplitude.  The  surface  of  the  cylinder  is 
covered  with  lampblack  before  using.  When  the  quill  is 
placed  in  contact  with  the  coated  cylinder,  the  latter  is  set 
to  rotating  and  the  fork  to  vibrating.  The  quill-point  will 
then  trace  on  the  cylinder  a  sinusoidal  curve,  and,  the 
number  of  vibrations  of  the  fork  per  second  being  known, 
we  have  an  accurate  scale  of  time.  If  the  time  to  be 
measured  is  greater  than  can  be  registered  on  one  revolu-. 
tion  of  the  cylinder,  the  cylinder  or  fork  is  given  a  motion 
of  translation  along  the  axis,  and  the  sinusoidal  curve  then 
becomes  a  helix,  and  the  whole  length  of  the  cylinder  can 
be  used. 

MARCEL  DEPREZ  REGISTERS. — The  record  is  made  as  fol- 
lows: Small  electro-magnets,  ee,  Fig.  21,  are  placed  in  front 


GUNPOWDER  AND   INTERIOR  BALLISTICS, 


97 


They  are  provided 


--A 


of  the  cylinder,  above  the  time-register, 
with  very  light  armatures,  /,  acted 
on  by  a  spring,  g,  which  is  almost  in 
equilibrio  with  the  magnetic  attrac- 
tion. A  point,  //,  connected  with  the 
armature,  rests  against  the  surface  of 
the  cylinder.  When  the  current  at 
a  target  is  broken,  the  correspond- 
ing armature  /  yields  to  the  action 
of  the  spring  g  and  is  drawn  aside 
quickly,  the  point  h  recording  the 
motion  on  the  cylinder  by  the  side 
of  the  time-scale.  The  number  of 
vibrations  of  the  fork  between  any 
two  breaks  divided  by  the  number 
per  second  gives  the  corresponding  time.  To  assist  in 
counting  vibrations,  the  quill  b,  Fig.  20,  is  first  allowed 
to  trace  a  simple  helix  before  the  fork  is  put  in  vibra- 
tion. The  quill-point  is  then  returned  to  its  starting-point. 
This  line  is  called  the  mean  helix.  If  the  targets  are  at 
such  a  distance  apart  that  the  current  which  is  broken  at 
one  point  may  be  restored  before  the  projectile  reaches  the 

next,  one  register  and  one  circuit 
will  be  sufficient.  If  the  targets 
are  too  close  together  for  this  res- 
toration of  current,  each  target 
must  have  its  own  current  and 
register.  The  registers  have  a 
motion  of  translation  in  common 
with  that  of  the  tuning-fork. 

BASHFORTH  TARGETS.  —  For 
restoring  the  current  as  above 
described,  the  simplest  device  is 
theBashforth  target,  invented  and 
used  by  the  Rev.  Francis  Bash- 
forth  in  his  celebrated  experi- 
FIG!  22'  merits  on  the  resistance  of  the  air 

to  the  motion  of  projectiles. 

This  target  (Fig.  22)  consists  of  a  series  of  wire  springs,  bd> 


9§  TEXI^-BOOK  OF  ORDNANCE  AND    GUNNERY. 

inserted  in  a  board.  On  the  front  of  this  board  are  brass 
plates,  ace,  having  oblong  holes  in  them  through  which  the 
springs  pass. 

The  springs  are  held  down  in  contact  with  the  lower 
side  of  the  holes  by  weights,  w  w,  attached  to  them  by 
strings.  The  current  entering  the  plate  a,  will  pass  through 
the  wire  spring  b  to  the  plate  c,  and  so  on.  When  one 
of  the  strings  is  cut  by  a  projectile,  the  corresponding 
spring  will  fly  up  to  the  upper  side  of  the  hole  in  the  brass 
plate  c,  and  the  current  will  be  broken  during  the  passage 
of  the  spring  from  bottom  to  top  of  hole,  and  will  be  made 
again  as  soon  as  the  spring  strikes  the  top. 

47.  Determination  of  Pressures  by  Experiment  —  Static  Method  — 

Discussion—  Conclusions. 
There  are  two  methods  of  measuring  a  force  or  pressure  : 

1.  The  Static  Method,   in    which    the  unknown    force   is 
balanced  by  a  known  resistance  ; 

2.  The  Dynamic  Method,  in  which  the  unknown  force  is 
determined  by  the  acceleration  which  it  communicates  to  a 
given  mass.     Its  measure  is,  from  mechanics, 

dv  dls 


STATIC  METHOD.  —  General  Principles.  —  The  general 
method  adopted  in  this  case  is  to  balance  the  unknown  force 
by  the  resistance  which  a  body  offers  to  deformation.  If  we 
have  a  cylinder  of  metal  of  known  length  and  diameter,  and 
uniform  in  quality,  and  apply  to  it  a  known  force  in  the 
direction  of  its  length,  the  cylinder  will  be  decreased  in 
length  by  a  certain  amount.  We  measure  accurately  this 
decrease  in  length  and  note  the  force  producing  it.  Pro- 
ceeding in  this  manner  we  can  form  a  table  one  column  of 
which  will  contain  the  decrease  in  length  of  the  cylinder, 
and  the  other  the  corrresponding  pressure  for  all  pressures 
within  the  limits  of  experiment.  From  this  table  a  curve 
may  be  constructed  whose  abscissas  give  the  pressures,  and 
the  ordinates  the  corresponding  compressions. 

Such  a  curve  is  called  the  "  tarage  "  of  the  cylinder. 


GUNPOWDER   AND    INTERIOR  BALLISTICS.  99 

If  now  a  cylinder  of  the  same  material  and  dimensions  be 
subjected  to  the  force  to  be  measured,  and  this  force  be 
applied  in  the  same  manner  as  that  producing  the  "  tarage," 
it  is  only  necessary  to  measure  the  compression  produced 
by  the  unknown  force,  and  find  from  the  "  tarage,"  or  from 
the  table,  the  corresponding  pressure. 

DISCUSSION. — The  pressure  we  wish  to  measure  is  that 
of  the  powder-gas.  This  gas  acts  upon  the  cylinder  to  be 
compressed,  through  the  medium  of  a  piston  whose  area  is 
exactly  known. 

This  piston  moves  in  a  cylindrical  channel,  and  its  head 
rests  against  the  cylinder  to  be  compressed,  the  gas  acting 
upon  the  opposite  end  of  the  piston  (see  Noble  crusher- 
gauge).  In  order  that  the  results  of  the  compression  may 
agree  with  those  of  the  "  tarage,"  the  mass  of  the  piston  and 
its  velocity  must  be  as  small  as  possible.  To  show  this:  At 
any  instant  let 

P  be  the  intensity  of  the  force  to  be  measured ; 

R,  the  resistance  to  deformation  offered  by  the  cylinder ; 

m,  the  mass  of  the  piston  ; 

v,  its  velocity  ; 

x,  the  length  of  path  passed  over  by  it. 

The  work  of  the  pressure  on  the  piston  over  the  path  x 
is 


/ 

t/o 


Pdx, 
and  that  of  the  resistance  over  the  same  path 


and  the  difference  between  these  is  the  energy  of  the  piston  ; 
hence 


In  order  that  P  =  R,  which  is  the  condition  sought,  we 
must  have  at  all  times 

=  o. 


L 


IOO  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Now  m  cannot  be  zero,  but  it  must  be  as  small  as  possi 
ble,  and  v  must  also  be  small.  The  former  condition  is 
attained  by  making  the  piston  small,  and  the  latter  by  com- 
pressing the  cylinder  before  firing  by  a  force  nearly  equal 
to  the  value  of  P  anticipated. 

CONCLUSIONS. — From  numerous  experiments  Sarrau 
concludes : 

1.  Gunpowder  is  the  only  explosive  which  under  ordi- 
nary conditions  produces  compressions  agreeing  with  the 
"  tarage." 

2.  This  conclusion  is  true  only  when  the  gauge  is  in  rear 
of  the  projectile.     In  the  powder-chamber  the  pressure  rises- 
from  zero  to  a  maximum  in  a  short  time,  but  the  time  is  ap- 
preciable.    Hence  the  application  of  the  pressure  resembles 
in    some    degree  that  of   the  force  producing   the  tarage. 
When,  however,  the  gauge  is  situated  in  front  of  the  base  of 
the  projectile,  the  gas  suddenly  strikes  it,  upon  the  passage  of 
the  projectile,  and  we  have  a  case  similar  to  that  of  the  high 
explosives,  and  the  same  rule  applies  as  with  them.   (See  3.) 

3.  For  the  high  explosives,  the  rate  of  application  of  the 
force  is  so  great  that  as  a  general  rule  the  maximum  press- 
ure is  measured  by  the  "  tarage  "  corresponding  to  one  half 
the  compression  of  the  cylinder. 

48.  Rodman  and  Noble  Gauges — Advantages  of  Noble. 

RODMAN  GAUGE. — The  Rodman  Pressure-gauge,  Fig. 
23,  consists  of  a  body  or  housing,  H,  which  is  a  receptacle 
for  all  the  working  parts.  A  copper  disk,  C,  is  placed  in 
the  housing,  and  a  knife,  K,  rests  against  it.  The  knife  is 
attached  to  the  piston  P,  which  fits  accurately  in  the  cylin- 
drical hole  in  the  housing.  The  housing  is  closed  by  a 
screw-plug,  /. 

The  gas  acts  on  the  end  P'  of  the  piston,  and  presses  the 
knife  into  the  copper  disk,  causing  it  to  make  a  cut,- whose 
length  measures  the  .pressure.  A  small  copper  cup,  c,  is 
placed  at  the  outer  end  of  the  piston  to  act  as  a  gas-check, 
and  prevent  the  entrance  of  gas  into  the  housing.  This 
gauge,  when  used,  is  placed  in  the  centre  of  the  bottom  of 
the  cartridge-bag  and  tied  to  it  with  a  string  around  the 


GUNPOWDER  AND   INTERIOR  BALLISTICS.  IOI 

groove  g.     When  in  the  gun,  it  must  rest  against  the  bottom 


FIG.  23. 

of   the   bore.     The  gauge   may  also  be  screwed   into  the 
breech-block,   or  walls   of   the   bore, 
in  which    case  it  is  threaded  on  the 
exterior. 

NOBLE  CRUSHER  GAUGE.  — This 
has  replaced  the  Rodman  gauge  gen- 
erally, for  reasons  which  will  appear 
later.  It  was  used  in  Noble  and  Abel's 
experiments.  It  consists  (Fig.  24)  of 
a  housing,  H,  closed  by  a  screw-plug, 
/,  and  forming  a  receptacle  for  the 
working  parts. 

These  consist  of  a  piston,  P,  mov- 
ing in  a  cylindrical  channel  as  shown, 
and  a  copper  cylinder,  C,  to  be  com- 
pressed, which  is  in  contact  with  the 
piston.  The  cylinder  is  central,  and 
kept  in  the  axis  of  the  housing  by  the 
spring  5. 

A  copper  cup,  c,  is  used  as  a  gas- 
check  as  in  the  Rodman,  and  an- 
other method  for  the  same  purpose,  called  "  air-packing. 


102  TEXT- BOOK  OF  ORDNANCE   AND    GUNNERY. 

is  also  employed.  A  series  of  grooves,  a  (Fig.  25),  are 
made  around  the  piston.  If  gas  enters  between  the  piston 
and  its  channel,  it  escapes  into  the 
first  groove,  and  by  expanding,  its  ten- 
sion is  diminished.  It  may  also  escape 


H 


a 


into  the  second  groove,  and  so  on,  and 
by   each  expansion  its  tension  is  still 
FIG.  25.  further   reduced    till    it    is   unable    to 

penetrate  into  the  body  of  the  housing.  The  action  of  the 
gauge  is  evident.  In  using  it,  the  piston  must  always  be  in 
contact  with  the  copper  cylinder. 

ADVANTAGES  OF  NOBLE  GAUGE. — i.  It  is  smaller  than 
the  Rodman,  since  the  copper  cylinder  is  smaller  than  the 
disk.  It  therefore  takes  up  less  room  in  the  gun.  The  mass 
of  the  piston  is  also  less  than  that  of  the  knife  and  piston  in 
the  Rodman. 

The  advantage  of  this  has  been  shown. 

2.  The  knife  of  the  Rodman  is  difficult  to  reproduce  if 
broken,  while  the  piston  of  the  Noble  can  always  be  dupli- 
cated. 

3.  The  copper  disk  offers  very  little  resistance  to  motion 
at  first,  while  that  offered  by  the  cylinder  is  more  nearly 
uniform. 

4.  The  cylinder  can  be  given  a  preliminary. compression, 
but  a  preliminary  cut  cannot  be  given  to  the  copper  disk. 

49.  Determination  of  Pressures  by  the  Dynamic  Method — Noble  and 
Abel's  Method  -Letard's  Apparatus — Sebert's  Velocimeter. 

In  this  method  the  pressure  is  determined  by  the  accel- 
eration of  a  known  mass.  The  mass  may  be  either  the  pro- 
jectile, the  gun,  or  a  piston  lodged  in  the  walls  of  the  bore, 
and  communicating  with  it  by  a  radial  channel. 

NOBLE  AND  ABEL'S  METHOD.— In  this  method  the  mo- 
tion of  the  projectile  is  used,  as  already  explained,  page  77,. 
and  the  result  is  given  by  equation  (150), 


GUNPOWDER   AND    INTERIOR   BALLISTICS.  103 

the  value  oi  ~  being  determined  by  calculation  from  data 

obtained  by  the  experiment. 

LETARD'S  APPARATUS.— To  avoid  piercing  the  walls  of 
the  bore,  as  in  Noble  and  Abel's  method,  this  apparatus  is 


—SHOT) 


rCJ 


FIG.  26. 

employed.  It  consists  (Fig.  26)  of  a  body  of  wood,  on  the 
front  of  which  is  a  metallic  ring,  b.  A  metal  bolt,  a,  passes 
through  the  wood  body  and  projects  to  the  rear,  its  head 
being  in  contact  with  the  ring  b.  A  pin,  c,  which  is  easily 
broken,  holds  the  bolt  a  in  place.  When  in  this  condition 
the  current  passes  through  the  ring  and  bolt. 

The  wood  body  is  attached  to  a  second  piece  of  wood, 
and  the  whole  is  placed  in  the  bore  of  the  gun,  and  secured 
against  the  wall  with  resin  or  cement.  When  the  projectile 
strikes  the  projecting  end  of  the  bolt  a,  the  pin  c  is  broken, 
and  the  bolt  driven  out,  thus  breaking  the  circuit. 

SEBERT'S  VELOCIMETER.— With  this  instrument  the  mo- 
tion of  the  gun,  or  of  the  projectile,  or  of  both,  may  be  used. 
The  general  principles  are  as  follows:  A  ribbon  of  steel  5 
(Fig.  27)  is  attached  to  the  trunnion  of  the  gun  by  the  rod  T 
and  the  gun  mounted  so  as  to  recoil  with  very  little  friction. 
As  recoil  takes  place,  the  ribbon  has  the  same  motion  as 
that  of  the  gun.  A  tuning-fork,  A,  whose  rate  of  vibration  is 


104 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


known,  is  fixed,  with  reference  to  the  gun,  above  the  ribbon, 
and  carries  a  quill-point,  b.  The  fork  is  made  to  vibrate  by 
electro-magnets,  c,  as  in  the  Schultz  Chronoscope,  and  dur- 
ing recoil  the  quill-point  traces  on  the  blackened  surface  of 
the  ribbon  a  sinusoidal  curve  which  is  the  scale  of  time. 
In  rear  of  the  tuning-fork  are  placed  several  Marcel-Deprez 
registers,  Ry  connected  with  Letard  interrupters  in  the  gun. 
When  the  projectile  passes  a  point  at  which  one  of  the  inter- 


FIG.  27. 

rupters  is  situated,  the  break  is  registered  on  the  steel  rib- 
bon beside  the  scale  of  time,  and  so  for  each  successive 
break.  The  number  of  vibrations  between  breaks,  divided 
by  the  number  of  vibrations  per  second  of  the  fork,  gives 
the  time  of  passage  of  the  projectile  over  the  distance  be- 
tween interrupters,  and  from  this  we  can  determine  the 
velocity.  From  these  velocities  we  can  determine  the  ac- 
celerations, and  hence  the  pressures,  using  the  mass  of  the 
projectile. 

Since  the  ribbon  contains  a  complete  record  of  the  mo- 
tion of  recoil  of  the  gun,  we  can  also  determine  velocities 
and  accelerations,  and  hence  the  pressures,  using  the  mass 
of  the  gun. 


CHAPTER   II. 

HIGH    EXPLOSIVES   AND   SMOKELESS  POWDERS. 
HIGH    EXPLOSIVES. 

50.  Definitions  and  Classification. 

An  Explosive  is  a  substance  which  is  capable  of  a  sudden 
change  from  a  solid  or  liquid  to  a  gaseous  state,  with  evolu- 
tion of  great  heat. 

A  High  Explosive  is  one  in  which  this  change  is  very 
rapid,  and  is  accompanied  by  a  crushing  or  shattering 
effect. 

A  Low  Explosive  is  one  in  which  the  change  is  relatively 
slow,  and  accompanied  by  a  propelling  or  pushing  effect. 
CLASSIFICATION. — Explosives  may  be  classed  into 

1.  Explosive  mixtures  ; 

2.  Explosive  compounds. 

Explosive  Mixtures  are  intimate  mixtures  of  certain  sub- 
stances which  are  in  themselves  inexplosive,  and  which 
undergo  no  chemical  change  till  the  moment  of  explosion. 
They  consist  generally  of  a  combustible  body,  such  as  car- 
bon, and  an  oxidizing  agent,  such  as  potassium  nitrate. 
The  best  example  is  gunpowder,  which  has  already  been 
discussed. 

Explosive  Compounds  are  chemical  compounds,  the  mole- 
cules of  which  are  explosive  in  themselves.  They  contain 
one  or  more  combustible  elements,  such  as  carbon  and  hy- 
drogen, together  with  the  oxygen  necessary  to  oxidize  these 
elements. 

The  constitution  of  the  molecule  is  more  or  less  unstable, 
and  when  heated  to  a  certain  degree,  the  molecule  breaks 
up  with  the  formation  of  the  gaseous  products  of  oxidation. 

The  most  important  explosive  compounds  are  the  or- 

105 


106  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

ganic  nitrates  or  nitric  ethers,  whose  composition  may  be 
represented  by  R-O-NQ2,  and  the  nitro-substitution  com- 
pounds, represented  by  R-NO2,  R  in  each  case  represent- 
ing the  hydrocarbon  radical. 

Both  are  derived  from  organic  substances  by  the  action 
of  nitric  acid, — th*e  former  from  complex  alcohols,  such  as 
glycerine,  etc.;  the  latter  from  certain  hydrocarbons, — by 
the  substitution  in  each  case  of  NO3  of  the  acid  for  H  of  the 
alcohol  or  hydrocarbon. 

Usually  from  each  substance  a  series  of  explosive  com- 
pounds can  be  made,  depending  upon  the  number  of  atoms 
of  H  replaced  by  NO2. 

In  the  explosive  mixtures,  relatively  great  distances  exist 
between  the  atoms  which  are  to  combine,  while  in  the  com- 
pounds each  molecule  constitutes  a  complete  explosive, 
and  hence  the  transformation  is  much  more  rapid  with  the 
latter. 

51.  Orders  of  Explosion— Berthelot's  Theory—Detonators. 

ORDERS  OF  EXPLOSION. — When  gunpowder  is  fired  in 
the  ordinary  manner  we  have  an  explosion  of  the  second 
order;  when  it  is  mixed  with  nitro-glycerine  and  fired,  we 
may  have  an  explosion  of  the  first  order,  or  a  detonation. 

The  difference  consists  in  the  time  necessary  to  produce 
the  chemical  change.  In  the  case  of  the  explosion  of  the 
"second  order,  the  time  is  appreciable  ;  in  the  case  of  detona- 
tion the  change  is  practically  instantaneous  throughout  the 
whole  mass  of  the  body. 

BERTHELOT'S  THEORY. — Berthelot,  the  great  French 
authority,  accounts  for  the  difference  in  these  orders  as  fol- 
lows :  Every  explosion  is  caused  by  heating  some  part  of 
the  substance  to  the  temperature  of  decomposition,  and 
this  temperature  is  transmitted  successively  to  all  parts  of 
the  body. 

In  the  case  of  explosions  of  the  second  order,  the  portion 
of  the  substance  first  heated  explodes ;  but  if  the  gases  have 
space  in  which  to  expand,  they  are  cooled  to  a  certain  ex- 
tent, and  heat  only  a  small  additional  portion  of  the  ex- 
plosive body  to  the  temperature  of  explosion.  This  new 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS.       TO/ 

portion  then  explodes,  and  the  cooling  again  takes  place; 
and  so  on,  the  explosion  being  propagated  successively 
from  layer  to  layer.  This  is  the  ordinary  case  with  gun- 
powder. 

Suppose,  now,  that  a  violent  shock  is  given  to  any  part 
of  the  explosive  body,  and  that  the  pressures  resulting  from 
this  shock  are  too  great  to  be  transmitted  throughout  the 
mass  of  the  explosive. 

The  energy  of  this  shock  will  be  transformed  into  heat, 
and  this  heat  will  affect  the  first  layers  of  the  explosive 
body  and  cause  them  to  be  suddenly  converted  into  gas,  or 
will  produce  detonation.  This  gas  being  suddenly  pro- 
duced, the  body  causing  the  shock  will  not  have  time  to  be 
displaced,  and  therefore  the  expansion  of  the  gas  thus  pro- 
duced will  cause  a  new  shock,  more  violent  than  the  first,  to 
the  layers  below. 

The  energy  of  this  shock  will  be  transformed  into  heat, 
and  will  cause  the  second  layer  to  detonate,  and  so  on. 

Hence  we  have  an  alternate  conversion  of  energy  into 
heat  and  of  heat  into  energy,  and  this  conversion  resembles 
the  propagation  of  a  sound-wave  in  a  given  medium,  except 
that  its  rate  of  travel  is  much  greater.  We  may  also  have 
a  combination  of  these  orders  of  explosion,  so  that  the  dis- 
tinction between  the  two  cannot  be  sharply  defined. 

Every  explosive  seems  capable  of  producing  the  two 
different  orders  of  explosion,  according  to  the  manner  in 
which  the  initial  heating  or  shock  is  given.  The  high  ex- 
plosives give  ordinarily  the  first  order  of  explosion,  the  low 
explosives  the  second  order. 

DETONATORS. — The  order  of  explosion  generally  de- 
pends on  the  intensity  of  the  initial  shock.  If  this  is  not 
great  enough,  the  explosive  may  burn  quietly,  or  give  an 
explosion  of  a  lower  order.  To  produce  this  initial  shock, 
a  small  quantity  of  some  violent  explosive,  called  a  detona- 
tor, is  required. 

The  principal  detonating  agent  in  use  is  fulminate  of 
mercury,, which,  on  account  of  its  great  force,  gives  rise  to  a 
high  temperature  when  the  initial  shock  is  converted  into 
heat. 


108  TEXT-BOOK  OF  ORDNANCE   AND    GUN  AERY. 

52.  Modes  of  Producing  Explosion — Fuzes — Detonation  by  Influence. 
An  explosion  of  the  second  order  may  be  produced  by 
shock,  friction,  the  direct  application  of  heat,  by  electricity 
or  by  an  ordinary  primer,  and  by  certain  chemical  or  physical 
changes;  but  to  produce  detonation  a  special  fuze,  called  a 
detonating  fuze,  is  generally  employed.  The  material  used  in 
these  fuzes  is  ordinarily  mercuric  fulminate,and  one 
form  is  shown  in  Fig.  28.  A  is  a  copper  shell ;  B, 
the  chamber  filled  with  mercuric  fulminate  ;  C, 
the  electric  wires  ;  D,  the  ends  of  these  wires ;  Ey 
\"D  the  platinum  bridge  which  is  heated  by  the  cur- 
rent ;  F,  the  sulphur  cement  holding  the  wires  and 
fulminate  in  place.  This  fuze  is  placed  in  the 
mass  of  the  explosive,  as  its  effect  is  weakened  if 
a  layer  of  air  is  interposed.  Other  varieties  of 
fuzes  are  used.  Those  fired  by  electricity  are 
classed  as  high  and  low  tension,  according  to  the 
kind  of  current  used  with  them. 

Mass  of  Fuze.  --  The  mass  of  the  detonator 
should  bear  a  certain  proportion  to  that  of  the 
explosive.  If  it  is  too  weak,  it  produces  a  low 
order  of  explosion  ;  if  too  strong,  it  may  scatter 
the  explosive. 

The  exception  to  the  rule  is  nitro-glycerine, 
which  detonates  equally  well  with  a  small  or  a 
large  primer ;  but  it  holds  for  gun-cotton,  and  for 
those  explosives  which  have  been  rendered  less 
sensitive  by  various  means. 

DETONATION  BY  INFLUENCE. — If  a  series  of 
cartridges  of  dynamite  or  gun-cotton  be  placed  at  certain 
distances  apart,  and  one  of  them  be  detonated  by  a  fulminate 
primer,  the  others  will  also  detonate.  This  is  called  "  deto- 
nation by  influence "  or  "sympathetic"  detonation.  It  ap- 
pears to  be  governed  by  the  following  laws : 

i  The  distance  apart  at  which  detonation  occurs  de- 
pends on  the  envelope  of  the  cartridges,  and  the  nature  of 
the  material  on  which  the  cartridges  rest.  If  the  initial 
cartridge  is  enveloped  in  a  non-resisting  material,  such  as 
a  paper  envelope,  the  influence  extends  much  further  than 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS.       109 

with  a  resisting  envelope.  If  the  cartridges  rest  on  a  re- 
sisting material,  as  an  iron  rail,  the  effect  is  propagated  to  a 
greater  distance  than  if  they  rest  upon  the  ground. 

2.  The  envelope  of  the  secondary  charges  should  be  as 
thin  and  elastic  as  possible,  in  order  to  oppose  the  minimum 
resistance  to  the  shock. 

3.  An  explosion  thus  propagated  will    become  weaker 
from  cartridge  to  cartridge,  and  may  even  change  its  order. 

4.  Similar  effects  are  observed  under  water. 

5.  The  shock  is  better  transmitted  by  a  liquid  than  by  a 
gas. 

6.  The  density  of  the  secondary  charges  should  be  as 
great  as  possible,  in  order  that  the  effect  may  not  be  reduced 
by  motion  among  the  particles. 

53.  Strength  of  an  Explosive  —  Potential  —  Force  —  Rapidity  of 
Reaction. 

STRENGTH. — An  explosive  must  be  considered  as  exert- 
ing pressure  and  having  potential  energy,  and  in  order  to 
estimate  its  strength,  and  its  value  for  different  purposes, 
we  must  be  able  to  determine  the  relative  values  of  the  pres- 
sure and  potential  for  each  explosive. 

Water  in  freezing  exerts  ^reat  pressure  if  confined,  and 
may  burst  the  walls  of  the  containing  vessel.  The  frag- 
ments, however,  will  not  be  projected  to  any  distance. 

In  this  case  we  have  a  great  pressure,  but  no  potential 
energy  or  capacity  to  do  work.  If  instead  of  water  a  high 
explosive  be  confined  in  the  envelope  and  detonated,  two 
effects  will  be  observed  :  the  walls  will  be  ruptured,  and  the 
fragments  thrown  violently  in  all  directions.  In  this  case 
we  have  the  pressure  required  to  rupture  the  walls,  and  the 
potential  energy  necessary  to  project  the  fragments. 

Again,  if  we  compare  equal  weights  of  large  and  small 
grained  powder  of  the  same  composition,  exploded  in  a 
closed  vessel,  it  is  evident  that  the  potential  is  the  same  for 
both,  since  the  products  and  the  quantity  of  heat  dis- 
engaged are  the  same ;  the  force  or  pressure  is  also  the 
same,  since  this  depends  solely  on  the  density  of  loading. 
The  effect  of  these  powders  is,  however,  very  different. 


110  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY 

The  small-grained  powder,  if  exploded  in  a  shell,  will 
burst  it  into  many  fragments  and  project  them  to  great  dis- 
tances, while  the  large-grained  powder  will  give  few  frag- 
ments and  small  propelling  force.  Similar  effects  are  ob- 
served with  different  classes  of  high  explosives,  and  depend 
on  the  rapidity  of  the  reaction  by  which  they  are  converted 
into  gas. 

The  strength  of  an  explosive,  then,  depends  on  — 

1.  Its  force  or  pressure; 

2.  Its  potential  ; 

3.  The  rapidity  of  its  reaction  or  conversion. 

FORCE  OR  PRESSURE.  —  The  force  of  an  explosive,  as 
already  defined  in  the  case  of  gunpowder,  is  the  pressure  ex- 
erted by  its  gaseous  products  per  unit  of  surface,  when  unit 
weight  of  these  products  is  confined  in  unit  volume.  The 
expression  for  it  in  the  case  of  gunpowder  is,  equation  (28), 

/•_    A^o^o. 

f~  ~ 


and  the  same  expression  measures  the  lorce  of  any  explosive, 
vt  being  the  specific  volume,  /0  the  atmospheric  pressure, 
and  T0  the  absolute  temperature. 

POTENTIAL.  —  The  potential  energy  of  an  explosive  is  the 
total  work  it  can  do,  when  the  products  are  indefinitely  ex- 
panded without  loss  of  heat,  all  the  heat  being  expended  in 
the  performance  of  work. 

Let  E  be  the  potential  energy  of  unit  weight  of  the  ex- 
plosive, J  the  mechanical  equivalent  of  a  heat-unit,  T9  the 
absolute  temperature  of  explosion,  and  K  the  mean  specific 
heat  of  the  products.  Then 


RAPIDITY  OF  REACTION.—  This  depends  on  the  rapidity 
with  which  the  chemical  transformation  is  propagated 
throughout  the  mass  of  the  explosive.  Certain  explosives, 
such  as  nitro-glycerine  and  gun-cotton,  have  very  great 
velocities  of  conversion,  and  they  may  be  regarded  as  un- 
dergoing an  instantaneous  change. 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS.       Ill 

This  change  being  so  rapid,  the  heat  is  employed  almost 
entirely  in  expanding  the  gases  and  performing  mechanical 
work.  Hence  these  substances  are  violent  explosives,  and 
shatter  everything  in  their  path. 

The  transformation  is  made  to  take  place  less  rapidly  by 
removing  the  particles  to  a  greater  distance  from  each  other, 
as  in  the  case  of  gunpowder,  which  then  decomposes  com- 
paratively slowly  and  exerts  a  pushing  effect  rather  than 
that  of  a  blow. 

It  is  evident  that  the  choice  of  an  explosive  depends  upon 
the  relative  values  of  these  three  elements.  If  an  explosive 
is  required  for  a  shell,  we  need  one  having  the  greatest  pos- 
sible potential  to  scatter  the  fragments,  a  relatively  small 
force,  so  as  not  to  break  it  into  very  small  fragments,  and 
gVeat  rapidity  of  reaction  in  order  that  all  the  gases  may 
be  formed  before  the  shell  breaks.  For  mining,  we  require 
moderate  force,  small  potential,  and  moderate  rapidity  of 
reaction,  etc. 

54.  Principal  Explosives — Gun-cotton. 

PRINCIPAL  EXPLOSIVES. — Gunpowder  may  be  regarded 
as  a  type  of  the  explosive  mixtures,  and  as  its  properties  are 
possessed  to  a  greater  or  less  extent  by  all  these  mixtures, 
the  high  explosives  only  will  be  considered  in  what  follows. 

The  principal  ones  in  use  for  military  purposes  are : 

1.  Gun-cotton; 

2.  Nitro-glycer  ine; 

3.  Dynamites; 

4.  Picric  acid  and  picrates ; 

5.  Fulminates  ; 

6.  Sprengel  safety  mixtures ; 

7.  Smokeless  powders. 

GUN-COTTON.— Its  chemical  formula  is  C6HTO,(ONO,),, 
and  it  is  formed  from  cotton  wool  by  the  action  of  strong 
nitric  acid.  The  reaction  is 

C.H A(OH).  +  3HN03  -  C.HtO,(ONO,).  +  3H.O. 

Cellulose.  Nitric  Acid. 

Sulphuric  acid  is  added  to  the  nitric  to  take  up  the  water 
and  prevent  the  dilution  of  the  later  acid,  which  would  give 


112  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

the  lower  orders  of  nitration,  such  as  collodion  cotton.  The 
method  of  preparing  it  is  described  in  chemistry. 

In  the  earlier  processes  of  manufacture  the  long  fibres 
of  cotton  were  used.  These  became  filled  with  the  acids, 
and  being  capillary  tubes,  it  was  found  impossible  to  wash 
them  out,  and  hence  the  product  was  unstable  and  liable  to 
spontaneous  decomposition.  Abel,  however,  improved  the 
process  of  manufacture  by  selecting  the  cotton  waste,  and 
cleaning  it  with  alkaline  washing,  and  especially  by  cutting 
up,  or  pulping  the  gun-cotton  after  it  had  been  partially 
freed  from  the  acids  employed  in  its  manufacture.  By  this 
operation  the  long  fibres  were  reduced  to  very  short  tubes 
which  could  be  thoroughly  washed.  A  final  washing  in 
alkaline  water  completed  the  neutralization  of  free  acids. 

Forms. — Gun-cotton  occurs  ordinarily— 

1.  In  the  form  of  wool,  like  the  original  cotton; 

2.  In  compressed  cylinders  and  slabs. 

The  first  form  is  that  in  which  the  cotton  was  used  up  to 
the  time  of  Abel's  improvement.  It  was  sometimes  twisted 
into  strands,  and  woven,  to  regulate  its  rate  of  burning. 

The  compressed  cylinders  are  made  by  the  action  of  a 
hydraulic  press  upon  the  pulped  and  washed  gun-cotton. 

Properties — Density. — Its  density  is  about  0.2  for  the  wool 
form  and  i.i  for  the  dry  compressed. 

Solubility. — It  is  insoluble  in  water,  alcohol,  or  sulphuric 
ether,  but  is  soluble  in  acetone  and  acetic  ether.  This  in- 
solubility in  alcohol  and  sulphuric  ether  distinguishes  it 
from  the  lower  orders  of  nitrated  cellulose,  which  are  soluble, 
giving  collodion. 

Effect  of  Foreign  Substances. — The  addition  of  water  de- 
creases the  sensitiveness  to  explosion.  The  addition  of 
paraffine  has  a  similar  effect,  with  the  advantage  that  it  does 
not  evaporate.  The  reason  for  this  decrease  in  sensitiveness 
is  that  the  water  or  paraffine  gives  a  certain  elasticity  and 
solidity  to  the  gun-cotton,  so  that  the  initial  shock  of  the 
detonator  is  propagated  through  a  much  greater  mass,  and 
consequently  its  local  energy  is  diminished. 

Nitre  is  sometimes  added  to  increase  the  supply  of 
oxygen,  which  is  deficient. 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS.       113 

Free  Acids.  —  These  cause  spontaneous  decomposition, 
with  elevation  of  temperature  and  increased  sensitiveness, 
so  that  explosion  frequently  results. 

The  presence  of  these  acids  formerly  caused  many  acci- 
dents. 

Effect  of  Heat  and  Cold. — As  a  general  rule,  the  sensitive- 
ness of  a  high  explosive  increases  with  the  temperature.  If 
wet,  the  application  of  heat  will  cause  the  evaporation  of  the 
water  and  thus  increase  the  sensitiveness  of  the  gun-cotton. 

Cold  will  cause  the  freezing  of  the  wet  compressed  gun- 
cotton  and  its  consequent  flaking  and  disintegration. 

Ignition. — A  temperature  of  about  180°  C.  is  required. 
If  the  cotton  is  dry  and  unconfined,  the  application  of  flame 
will  cause  it  to  burn  quickly.  If  the  mass  is  large,  an  explo- 
sion may  occur,  but  it  will  be  ordinarily  of  a  low  order.  If 
wet,  the  cotton  will  burn  when  unconfined,  only  in  successive 
layers  as  they  become  dry. 

Detonation. — Dry  gun-cotton  is  detonated  by  a  fulminate 
fuze. 

Wet  or  paraffined  gun-cotton  requires  a  large  detonator  or 
an  initial  priming  charge  of  dry  cotton  with  a  fulminate  fuze. 

Reaction. — The  reaction  on  explosion  is 

2C.H701(ONO,)i  =  ;H20  +  3CO,  +  9CO  +  6N. 

There  is  evidently  a  deficiency  of  oxygen,  and  hence  of 
potential  energy,  and  therefore  nitre  is  sometimes  added  as 
before  stated. 

Use  in  Blasting. — From  the  CO  given  off  it  is  disadvan- 
tageous in  blasting  unless  a  nitrate  be  added.  It  has  also 
the  disadvantage  of  being  of  comparatively  low  density  and 
solid,  and  hence  it  cannot  be  introduced  so  readily  into  bore- 
holes, nor  in  such  large  quantities  as  other  explosives  which 
are  plastic  or  have  higher  densities.  It  is,  however,  very  safe. 

Use  for  Military  Purposes.— -It  has  been  used  for  charging 
torpedoes,  for  bursting  charges  for  shell,  and  for  destroying 
obstacles  such  as  walls,  palisades,  guns  and  carriages,  etc. 

Storage.— It  is  best  stored  wet,  as  under  these  conditions  it 
is  perfectly  safe.  It  should  not,  however,  be  exposed  in  this 
state  to  a  freezing  temperature  on  account  of  disintegration.. 


114  TEXT  BOOK  OF  ORDNANCE  AND    GUNNERY. 

55.  Nitre-glycerine. 

Its  chemical  formula  is  C.,Hr,(  ()NOa\  ,  and  it  is  formed  by 
the  action  of  strong  nitric  acid  upon  glycerine. 

The  reaction  is 


C.H.(OH).  +  3HN03  =  C.H.(ONOJ.  +  3H,O. 

Glycerine  Nitric  acid 

Sulphuric  acid  is  added  to  the  nitric,  as  in  the  case  of 
gun-cotton,  to  take  up  the  water  formed  in  the  reaction. 

The  method  of  preparing  it  is  to  add  the  glycerine  slowly 
to  the  mixture  of  acids  ;  to  keep  the  mixture  cool  by  cooling 
coils  in  the  vessel,  and  by  passing  a  current  of  air  through  it, 
which  also  insures  a  thorough  mixture  ;  and  to  wash  the  pro- 
duct thoroughly  with  water  to  which  a  small  quantity  of 
alkali  is  added,  to  insure  the  removal  ot  free  acid. 

Form.  —  Nitroglycerine  when  hrst  made  is  in  the  form  of 
an  opaque,  white,  oily  liquid,  becoming  colorless  with  time. 

Properties  —  Density.  —  Its  density  is  1.6. 

Solubility.  —  It  is  very  slightly  soluble  in  a  large  quantity 
of  cold  water.  It  is  freely  soluble  in  alcohol,  ether,  chloro- 
form, and  slightly  in  glycerine. 

It  has  a  sweet,  pungent,  aromatic  taste  ;  is  poisonous,  and 
causes  headache. 

Heat  and  Cold.  —  It  freezes  at4°.4  C.  to  a  white  crystalline 
solid,  and  is  almost  inexplosive  in  this  condition  by  ordinary 
means,  unless  a  small  mass  be  acted  upon  by  a  shock. 

When  frozen,  it  is  thawed  at  a  temperature  of  37°.  7  C.  by 
placing  the  vessel  containing  it  in  another  of  water  at  this 
temperature. 

Free  Acids.  —  These  cause  its  decomposition,  as  in  the 
case  of  gun-cotton,  and  render  it  more  sensitive  to  friction 
and  percussion,  and  hence  they  must  be  carefully  removed. 

Ignition.  —  Its  temperature  of  ignition  is  about  the  same 
as  that  of  gun-cotton,  180°  C. 

If  unconfined  and  subjected  to  a  blow,  the  particle  struck 
will  explode,  and  scatter  the  remainder. 

If  confined  and  struck,  it  will  detonate  ;  when  unconfined, 
in  small  masses,  the  application  of  flame  causes  it  to  burn 
rapidly  without  explosion. 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDEKS.       11$ 

Detonation.— It  is  detonated  by  mercuric  fulminate,  and 
the  detonator  should  be  placed  in  the  liquid.  If  frozen,  it 
may  also  be  detonated,  but  the  action  is  generally  less 
violent,  owing  to  incomplete  conversion. 

Reaction. — The  reaction  on  explosion  is 

2C3H6(ONOa),  -  6C02  +  6N  +  5H,O  +  O. 

Here  we  have  an  excess  of  oxygen,  and  the  reaction, 
following  a  general  law,  is  always  stable. 

Use  in  Blasting. — Nitro-glycerine  is  one  of  the  strongest 
of  the  high  explosives,  possessing  great  force,  potential,  and 
rapidity  of  reaction.  Owing  to  its  liquid  form  it  can  be 
poured  into  holes  of  any  shape,  provided  they  do  not  com- 
municate with  fissures,  and  from  its  great  rapidity  of  re- 
action, the  depth  of  the  hole  may  be  decreased,  and  no  tamp- 
ing except  water  is  required.  It  is  therefore  a  valuable 
agent  for  blasting,  but  owing  to  its  liquid  form  it  is  very 
unsafe  in  handling,  as  it  is  liable  to  leak,  and  thin  films  of  it 
may  be  easily  exploded.  For  this  reason,  except  for  special 
purposes,  it  is  now  generally  replaced  by  dynamite. 

Use  for  Military  Purposes. — The  same  remarks  apply  in 
this  case  as  for  blasting. 

Storage. — If  possible  nitro-glycerine  should  be  kept  frozen, 
and  should  be  transported  and  handled  in  this  state,  being 
thawed  before  using. 

Test  for  Purity.  —  Free  acid  may  be  detected  by  using  blue 
litmus-paper.  The  acid  will  redden  it. 

56.  Dynamite— With  Inert  Base. 

Owing  to  the  dangers  involved  in  the  transportation, 
handling,  and  storage  of  nitro-glycerine  as  previously  noted, 
efforts  were  made  to  find  an  absorbent  for  it,  so  that  it  could 
be  given  a  solid  form.  The  addition  of  these  absorbents  has 
given  rise  to  dynamite  and  various  other  derivatives  of 
nitro-glycerine. 

Absorbents  Classified.— These  may  be  classified  into:  I. 
Inert ;  2.  Chemically  active. 

INERT  ABSORBENTS — DYNAMITE  No.  i. — The  most  im- 
portant of  the  inert  bases  is  kieselguhr,  a  siliceous  infusorial 


Il6  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

earth  which  is  porous,  and  will  absorb  and  retain  about  three 
times  its  weight  of  nitro-glycerine. 

When  it  absorbs  about  75  per  cent  of  nitro-glycerine,  the 
product  is  called  dynamite  No.  I. 

Form. — It  is  either  granular,  or  in  compressed  cylinders, 
wrapped  in  paraffined  paper. 

Properties — Density. — Its  density  is  about  1.5  to  1.6. 

Heat  and  Cold. — Dynamite  freezes  at  4°.4C.,  and  in  this 
condition  is  detonated  with  great  difficulty  when  solid,  but 
when  loose  it  may  be  detonated,  the  explosion  being  less 
violent.  If  frozen,  it  must  be  thawed  before  exploding,  and 
this  should  be  done  very  carefully,  as  in  common  with  all 
preparations  of  nitro-glycerine  it  becomes  more  sensitive  as 
it  is  heated.  At  all  high  temperatures  the  nitro-glycerine 
exudes,  and  hence  the  dynamite  becomes  dangerous. 

Free  Acids. — These  are  very  dangerous,  and  the  same  re- 
marks apply  as  to  nitro-glycerine. 

Detonation. — A  fuze  of  fulminate  of  mercury  is  used,  which 
must  be  placed  in  the  mass  of  the  cartridge. 

Reaction. — This  is  the  same  as  for  nitroglycerine. 

Use  in  Blasting. — It  has  been  found  very  useful  in  blasting 
on  account  of  safety  in  handling.  The  potential  is  dimin- 
ished by  the  presence  of  the  silica,  and  hence  its  action  is 
less  violent,  and  its  effects  more  distributed.  By  regulating 
the  percentage  of  nitro-glycerine  present,  this  effect  may  be 
still  further  modified. 

Use  for  Military  Purposes. — In  the  U.  S.  service,  Dynamite 
No.  i  is  used  for  charging  torpedoes,  and  may  be  regarded 
as  the  standard  high  explosive  for  this  purpose.  General 
Abbott  of  the  U.  S.  Engineers  has  made  a  series  of  researches 
upon  this  subject,  and  has  deduced  formulas  for  the  inten- 
sity of  different  explosives  when  used  under  water.  (See 
"  Professional  Papers,  Corps  of  Engineers,"  No.  23 — 1881.) 

Storage. — Dynamite  No.  i  is  stored  in  boxes  of  wood,  in 
magazines  free  from  dampness,  and  no  fulminate  caps  or 
primers  should  be  stored  with  it. 

57.  Dynamite  with  Chemically  Active  Bases. 

Instead  of  an  inert  base,  a  combustible  one  may  be  used, 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS.       11? 

which  is  capable  of  combining  with  the  excess  of  oxygen  of 
the  nitro-glycerine  and  thus  increasing  the  potential. 

Various  substances  have  been  used  for  this  purpose. 

90  per  cent  of  nitro-glycerine  and  10  per  cent  of  charcoal 
form  carbo-dynamite.  Sawdust,  treated  with  superheated 
steam,  becomes  a  jelly,  and  is  capable  of  absorbing  a  large 
quantity  of  nitro-glycerine.  Other- compounds  of  the  same 
class  are  also  found. 

On  the  other  hand,  by  using  a  nitrate  or  chlorate  mixture 
as  a  base,  additional  effect  is  obtained  by  inducing  a  higher 
order  of  explosion  in  the  base.  When  gunpowder  is  used 
as  an  absorbent,  the  detonation  of  the  nitro-glycerine  causes 
the  detonation  of  the  powder.  Potassium-chlorate  mixtures 
are  also  used  for  this  purpose,  but  are  generally  regarded  as 
dangerous. 

High  Explosive  Bases. — The  most  important  of  these  com- 
pounds is  explosive  gelatine  or  "  gum-dynamite." 

It  has  been  shown  that  when  gun-cotton  detonates,  there 
is  a  deficiency  of  oxygen,  and  in  the  case  of  nitro-glycerine 
there  is  an  excess  of  it. 

If  these  two  explosives  are  mixed  in  such  proportions  as 
to  have  the  excess  of  oxygen  in  the  one,  neutralize  the  defi- 
ciency in  the  other,  we  have  a  considerable  increase  of 
potential.  The  result  is  best  realized  in  a  substance  called 
explosive  gelatine  or  gum-dynamite,  which  was  invented  by 
the  Swedish  engineer  Nobel. 

It  is  made  by  dissolving  7  parts  of  a  special  grade  of 
soluble  gun-cotton  in  93  parts  of  nitro-glycerine,  by  the  aid 
of  heat. 

For  military  purposes  about  4  per  cent  of  camphor  is 
added  to  decrease  its  sensitiveness. 

Form. — It  is  a  translucent  jelly  of  a  yellowish  or  dark 
brown  color,  which  may  become  in  time  hard  and  opaque. 

Properties— Density.— Its  density  is  1.6. 

Solubility.— It  is  insoluble  in  water  and  is  unaffected  by 
it. 

Heat  and  Cold.—\i  heated  slowly  to  204°  C,  it  explodes; 
and  it  freezes  at  low  temperatures. 

Ignition.— When  ignited  unconfined  it  burns  readily,  but 


Il8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

does  not  explode  ;  but  if  confined,  explosion  occurs.  It  is  not. 
affected  by  shock,  and  bullets  have  been  fired  through  it 
without  producing  explosion. 

Detonation. — For  detonation  a  special  primer  is  required, 
and  the  strength  of  the  primer  must  be  increased  as  the 
sensitiveness  of  the  gelatine  is  decreased. 

Use  for  Military  Purposes. — It  has  been  tried  as  a  bursting 
charge  for  shells;  but  as  it  requires  a  large  primer,  the  ad- 
vantages of  the  decrease  in  sensitiveness  of  the  explosive 
are  lost  by  the  increase  of  sensitiveness  of  the  primer. 

Storage. — Some  doubt  exists  as  to  the  stability  of  this 
compound,  and  the  effect  upon  its  sensitiveness  of  the  evap- 
oration of  the  camphor. 

58.  Picric  Acid  and  Picrates — Fulminates. 

The  chemical  formula  for  picric  acid  or  tri-nitro-phenol 
is  C6H2(NO2)3OH,  and  it  is  formed  by  the  action  of  nitric 
acid  on  carbolic  acid.  The  reaction  is 

C.H.OH  +  3HNO,  =  C.H.(NO,).OH  +  3H.O. 

Form. — It  occurs  in  yellow  crystals  which  are  slightly 
soluble  in  water.  It  explodes  when  heated  rapidly,  but  is, 
ordinarily  not  used  as  an  explosive  by  itself,  and  is  only  of 
importance  from  its  compounds. 

Potassium  Pier  ate.  —  This  salt  is  a  violent  explosive. 
Mixed  with  nitre  and  charcoal  and  grained,  it  forms  Desig- 
nolle's  powder,  which  has  been  used  for  small  arms  and 
cannon,  and  also  for  torpedoes,  with  good  results,  but  it  is 
expensive,  and  some  cases  of  premature  explosions  have  been 
noted. 

Ammonium  Pier  ate. — This  is  less  sensitive  than  the  potassa. 
salt,  and  burns  without  explosion  in  the  air.  Mixed  with 
nearly  equal  parts  of  nitre,  it  forms  Brugere's  powder,  which 
has  about  twice  the  strength  of  ordinary  gunpowder,  but  is 
expensive,  somewhat  hygroscopic,  and  too  violent  for  small 
arms. 

The  picrates  form  the  bases  for  certain  smokeless 
powders. 

Emmens  Acid. — This  acid  is  said  to  be  formed  by  the 
action  of  nitric  acid  upon  picric  acid. 


HIGH   EXPLOSIVES   AKD    SMOKELESS   POWDERS.       1  19 

Emmcnsitc  is  a  mixture  of  emmens  acid  and  sodium  or 
ammonium  nitrate.  It  is  yellow  and  crystalline  in  appear- 
ance,  and  is  used  in  mining  and  as  a  substitute  for  gun- 
powder, both  as  a  propelling  agent  and  for  charging  shells. 
It  is  much  stronger  than  gunpowder,  is  smokeless,  and 
almost  insensitive  to  shock. 

It  is  hygroscopic,  and  its  stability  after  long  storage  is 
not  yet  well  settled.  It  was  invented  by  Dr.  Emmens,  and 
is  stHl  undergoing  trial. 

Melinite.  —  This  French  explosive  is  generally  supposed 
to  be  a  mixture  of  gun-cotton  with  picric  and  cresylic  acids 
dissolved  in  ether. 

FULMINATES.  —  The  most  important  is  mercury  fulminate, 
the  chemical  formula  for  which  is  HgCsNQO2.  It  is  formed 
by  the  action  of  alcohol  upon  mercury  nitrate.  The  reac- 
tion is  rather  complex,  and  may  be  found  in  the  chemistry. 

Form.  —  It  is  in  fine  gray  crystals. 

Properties  —  Density.  —  Its  density  is  4.42. 

Solubility.  —  It  is  insoluble  in  water,  not  affected  by  the 
air,  and  is  poisonous. 

Water.  —  When  saturated  with  water  it  is  inex  plosive, 
and  hence  it  is  always  kept  under  water  for  safety. 

Detonation.  —  When  dry  it  is  very  sensitive  to  a  blow  and 
detonates  with  violence,  and  also  when  heated  to  182°  C. 
or  when  subjected  to  friction,  or  to  contact  with  any  ignited 
body,  or  to  the  action  of  the  electric  'spark. 

Reaction.  —  The  reaction  on  explosion  is 


t  —  The  great  value  of  this  explosive  is  as  a  detonator 
for  the  other  high  explosives.  Its  effects  are  due  to  its  great 
force,  since  the  volume  of  gas  given  off  is  very  great  ;  and 
also  to  its  high  density,  in  consequence  of  which  a  large 
mass  is  contained  in  a  small  volume.  The  gases  also  are 
not  subject  to  dissociation,  and  hence  impart  all  their  energy 
to  the  explosive  to  be  detonated.  It  is  said  to  have  ten 
times  the  force  of  gunpowder.  Being  comparatively  low 
in  potential,  an  oxydizing  agent  is  sometimes  added  when 
the  primer  is  at  a  distance  from  the  charge. 


120  TEXT- BO  OK  OF  ORDNANCE  AND    GUNNERY. 

Storage. — It  must  be  kept  under  water  for  safety,  and 
must  not  be  allowed  to  come  in  contact  with  a  metallic  sur- 
tace,  as  it  then  tends  to  decompose.  Hence  percussion-caps 
are  varnished  before  it  is  placed  in  them.  It  must  not  be 
stored  with  high  explosives. 

59.  Nitro-Benzines— Sprengel  Safety  Mixtures. 

NITRO-BENZINES. — These  are  formed  by  the  action  of 
nitric  acid  on  benzine,  and  we  have  the  mono-,  di-,  and  tri- 
nitro-benzines  resulting. 

They  are  not  explosive,  but  are  used  in  the  manufacture 
of  a  class  of  explosives  called  Sprengel  safety  mixtures. 

SPRENGEL  SAFETY  MIXTURES. — These  were  invented  by 
Dr.  Sprengel ;  the  idea  being  to  mix  an  oxydizing  with  a 
combustible  agent  at  the  time  it  is  to  be  used,  the  constituents 
being  each  non-explosive  before  mixture,  and  therefore  safe 
to  handle  and  transport. 

Rack-a-rock  is  a  Sprengel  mixture  of  liquid  mono-nitro- 
benzine  and  potassium  chlorate.  If  the  cartridges  are  kept 
awhile,  their  sensitiveness  to  friction  or  percussion  increases. 
This  explosive  was  used  at  Hell  Gate  in  1885  ;  240,000  Ibs. 
of  it  being  exploded  together  with  42,000  Ibs.  of  dynamite. 

Hellhoffite  is  a  mixture  of  di-nitro-benzine  and  nitric  acid. 
It  has  been  used  as  a  bursting  charge  for  shells,  by  plac- 
ing the  components  in  separate  vessels  in  the  shell,  and  caus- 
ing their  mixture  automatically,  either  during  its  flight  or  on 
impact. 

Bellite  is  a  mixture  of  tri-nitro-benzine  with  ammonium 
nitrate.  It  is  not  sensitive  to  blows  or  friction,  is  chemically 
stable,  and  can  be  stored  and  transported  without  change  or 
danger. 

Another  class  of  explosives  of  the  same  kind  are  the 
flameless  explosives,  which  when  confined  and  detonated, 
evolve  gases  which  quench  any  flame.  They  are  especially 
useful  in  mines  where  fire-damp  is  prevalent. 

Roburite  is  one  of  the  class  of  flameless  explosives,  made 
by  mixing  ammonium  nitrate  and  chlorinated  di-nitro-ben- 
zine, and  is  a  yellowish  powder.  It  is  flameless  because  the 
ingredients  are  so  proportioned  as  to  cause  complete  oxida- 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS,       121 

tion,  and  the  products  of  combustion  are  carbon  dioxide, 
water,  nitrogen,  and  HC1;  the  gases  given  off  quenching  any 
flame  that  may  be  produced. 

Many  other  explosives  of  this  class  are  made,  and  their 
composition  may  be  found  in  "  The  Dictionary  of  Ex- 
plosives," by  Major  J.  P.  Cundill. 


SMOKELESS  POWDERS. 

60.  Changes  in  Black  Powders  —  Early  History  of  Smokeless 
Powders. 

CHANGES  IN  BLACK  POWDERS.— A  general  idea  has  been 
given  previously  of  the  history  of  gunpowder,  and  the 
changes  made  in  it.  It  was  found  to  be  too  strong  even  for 
modern  guns  in  the  small-grained  form,  and  hence  Rodman 
conceived  the  idea  of  suiting  the  grain  to  the  calibre. 

His  perforated  powder  was  also  designed  with  the  idea 
of  burning  on  an  increasing  surface,  and  thus  decreasing  the 
volume  of  the  gas  emitted  at  first,  and  hence  the  maximum 
pressure. 

No  change  had  been  made  in  the  components  of  the 
powder.  Later  still  these  changes  in  form  were  combined 
with  changes  in  the  nature  of  the  materials,  and  their  pro- 
portions. In  the  cocoa-powder  the  nature  of  the  charcoal 
was  changed,  as  were  also  the  proportions  of  nitre,  sulphur, 
and  charcoal,  and  certain  carbo-hydrates  were  introduced. 

While  these  changes  made  the  powder  slower,  they 
necessitated  larger  charges.  This  increased  the  cost,  oc- 
cupied a  greater  volume  of  bore,  and  thus  reduced  the  path 
over  which  the  gases  worked,  and  necessitated  long  bores, 
and  also  gave  great  volumes  of  smoke. 

With  small  arms,  when  the  calibre  was  reduced  to  0.30, 
the  length  of  the  bullet  remaining  the  same,  it  became  neces- 
sary, in  order  to  obtain  an  increase  in  velocity,  to  increase 
the  mean  pressure  per  unit  of  area  of  the  projectile,  and 
hence  to  adopt  some  agent  having  better  ballistic  qualities 
than  the  old  powders.  Increased  charges  of  compressed 
black  powders  were  first  tried,  but  they  gave  high  and 


122  TEXT- BOOK   OF  ORDNANCE  AND    GUNNERY. 

irregular  pressures  and  relatively  lower  velocities  than  with 
the  old  charges. 

EARLY  HISTORY  OF  SMOKELESS  POWDERS. — To  obviate 
these  defects  a  new  explosive  was  sought,  which  would  in- 
crease the  velocities,  without  increasing  the  pressures  beyond 
safe  limits.  Naturally  the  high  explosives  were  tried,  and 
of  these  the  most  promising  was  gun-cotton.  It  was  known 
that  this  gave  no  smoke,  that  it  burned  freely  when  uncon- 
fined,  but  that  it  detonated  when  confined.  Attempts  were 
therefore  made  to  regulate  its  burning,  by  twisting  it  into 
strands  and  winding  these  on  the  exterior  of  a  hollow  wood 
cylinder,  so  that  the  cartridge  thus  made  would  fit  the 
chamber  of  the  gun.  It  was  supposed  that  when  sufficient 
pressure  was  developed,  the  cylinder  would  crush,  and  thus 
give  a  very  much  larger  volume  for  the  gases  to  expand  in, 
and  hence  prevent  detonation.  It  wras  found,  however,  that 
detonation  did  occur,  with  destruction  of  the  gun,  and 
attempts  in  this  direction  were  abandoned. 

Another  method  was  to  mix  gun-cotton  with  ordinary 
cotton.  The  two  were  after  mixture  subjected  to  a  strong 
compression,  but  it  was  difficult  to  obtain  a  homogeneous 
mixture,  the  velocities  were  not  increased,  and  the  gun- 
cotton  still  detonated. 

An  attempt  was  also  made  to  place  a  charge  of  black 
powder  in  front  of  the  charge  of  gun-cotton.  The  projec- 
tile was  started  by  the  burning  of  the  black  powder,  and 
then  the  gun-cotton  was  inflamed. 

This  plan  gave  excessive  pressures  in  practice,  and  was 
soon  abandoned. 

Abel's  compressed  cotton  was  also  tried  with  the  same 
results,  and  gun-cotton  was  then  abandoned  as  a  propelling 
agent.  This  was  about  1884. 

61.  Modification  of  Gun-cotton— Effect  of  Calibre. 

MODIFICATION  OF  GUN-COTTON. — In  all  the  early  trials 
of  gun-cotton  no  essential  modification  of  its  physical  con- 
dition was  attempted. 

The  fibres  of  the  gun-cotton  were  not  compact,  and  on 
being  subjected  to  the  action  of  a  highly-heated  gas,  the 


HIGH  EXPLOSIVES   AND    SMOKELESS  POWDEKS,       12$ 

flame  readily  penetrated  all  parts  of  the  mass,  raising  it  to 
the  temperature  of  explosion,  and  detonation  followed. 

In  1884  ^  was  proposed  to  dissolve  the  gun-cotton  in 
some  solvent,  which  could  afterwards  be  evaporated,  leav- 
ing a  compact  horny  substance,  which  would  resist  the 
penetration  of  flame,  and  burn  regularly.  This  was  the 
first  step  in  the  successful  manufacture  of  smokeless  powder. 

EFFECT  OF  CALIBRE. — With  black  or  nitrate  powders,  as 
has  been  shown,  the  size  of  the  grain  must  increase  with  the 
calibre  for  all  large  guns,  but  for  all  small  arms  the  same 
powder  (small-arms)  may  be  used  with  good  results. 

With  smokeless  powders,  however,  each  change  in 
calibre  of  the  small  arm  requires  a  change  in  the  powder 
used.  This  may  be  explained  as  follows :  As  the  calibre 
decreases,  the  length  of  the  bullet  remaining  constant,  while 
its  weight  decreases,  it  is  necessary  to  increase  the  initial 
velocity  of  the  projectile  to  obtain  superior  ballistic  results, 
and  this  increase  of  velocity  can  only  be  obtained  by  an  in- 
crease  of  pressure  per  square  inch  of  the  powder-gas. 

To  obtain  this  increase  the  physical  qualities  of  the 
smokeless  powder  are  modified  so  as  to  obtain  a  quicker 
powder,  and  this  is  accomplished  by  stopping  the  solution 
of  the  cotton  at  the  proper  point,  and  by  decreasing  the 
thickness  of  the  grain.  For  the  larger  calibres  the  solution 
of  the  cotton  is  more  complete  and  the  grains  thicker. 

Those  physical  qualities,  therefore,  which  principally 
affect  the  velocities  and  pressures  given  by  the  powder  are : 

1.  Its  degree  of  solution  or  density  ; 

2.  Its  thickness,  or  least  dimension  of  grain  ; 
both  of  which  regulate  its  burning. 

In  order  to  increase  the -pressure  per  unit  of  area,  a 
proper  combination  of  these  qualities  is  required  for  each 
particular  calibre,  and  this  requires  a  special  powder  for 
each  gun. 

62.  Operations  in  the  Manufacture  of  Smokeless  Powder— Solution. 

OPERATIONS.— The  principal  operations  in  the  manufac- 
ture of  a  smokeless  powder  of  the  nitro-cellulose  class  are : 

I.  Preparation  of  the  nitro-cellulose; 


124  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

2.  Solution  of  the  nitro-cellulose  in  a  proper  solvent ; 

3.  Compression  of  the  material  after  evaporation  of  the 
solvent ; 

4.  Rolling  into  sheets  or  pressing  into  rods  or  tubes  ; 

5.  Cutting  up  the  sheets,  rods,  or  tubes  into  grains ; 

6.  Drying  the  grains. 

SOLUTION. — The  principal  precautions  to  be  taken  in 
this  operation  are,  to  avoid  the  formation  of  lumps  or  undis- 
solved  particles  of  nitro-cellulose ;  to  have  the  solvent  act 
regularly ;  and  to  prevent  the  cotton  from  collecting  in 
masses,  so  that  the  solvent  cannot  readily  penetrate  it.  If 
the  powder  is  to  be  quick,  the  cotton  must  not  be  com- 
pletely dissolved,  and  hence  the  operation  must  be  stopped 
at  the  proper  time,  which  requires  great  delicacy  in  manip- 
ulation. 

In  the  operation,  the  gun  cotton  must  not  be  plunged  in 
the  solvent,  but  the  latter  must  be  poured  over  the  cotton. 
For  this  purpose  the  cotton,  which  is  finely  divided,  is 
placed  in  layers  of  the  proper  thickness,  in  ebonite  pans  of 
slight  depth.  These  are  enclosed  in  a  glass  vessel,  and  the 
solvent  added  in  the  form  of  a  spray.  The  gun-cotton 
gradually  dissolves,  or  rather  becomes  gelatinized  ;  the  sup- 
ply of  the  solvent  is  then  stopped,  and  the  solution  allowed 
to  proceed  to  the  proper  degree.  A  current  of  warm  air  is 
then  passed  over  the  gelatinized  gun-cotton,  carrying  off  the 
solvent  in  a  state  of  vapor,  which  is  afterwards  condensed 
in  a  cool  vessel.  In  this  manner  the  drying  of  the  powder 
is  assisted,  and  the  solvent  which  is  removed  can  be  used 
again.  The  cost  of  these  powders  depends  principally 
upon  the  solvent,  and  hence  it  is  important  to  collect  as 
much  of  it  as  possible. 

63.  Compression  and  Rolling — Cutting  Up — Drying. 

COMPRESSION.  —  During  the  evaporation  of  the  solvent, 
bubbles  are  formed,  the  effect  of  which  is  to  render  the 
mass  more  or  less  porous  in  places.  This  causes  irregular 
density,  and  hence  in  the  same  sheet  some  parts  would  burn 
more  quickly  than  others.  It  is  necessary,  therefore,  to 
get  rid  of  these  bubbles. 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS.       12$ 

The  thickness  of  the  sheet,  after  the  solvent  has  evapo- 
rated, is  not  uniform,  as  it  is  impossible  to  spread  the  cotton 
regularly  before  it  is  acted  on  by  the  solvent.  This  thick- 
ness is  very  important,  as  affecting  the  ballistic  properties  of 
the  powder. 

To  get  rid  of  the  bubbles  and  at  the  same  time  regulate 
the  thickness,  the  sheet  is  subjected  to  strong  pressure, 
which  is  kept  up  for  some  time.  This  pressure  has  also  the 
effect  of  completing  the  solution  of  certain  parts  which  were 
not  completely  dissolved. 

ROLLING. — The  sheet  is  then  passed  between  two  rolls  of 
polished  bronze.  The  upper  roll  must  be  so  arranged  that 
its  weight  will  not  rest  upon  the  sheet.  In  this  way  when 
the  sheet  has  reached  its  proper  thickness  it  will  not  be 
reduced  further. 

The  reduction  to  the  required  thickness  is  gradual,  so  as 
not  to  tear  the  surfaces.  In  general  three  or  four  successive 
passes  through  the  rolls  are  necessary. 

CUTTING  UP. — Black  powder  is  grained,  but  this  opera- 
tion is  impossible  with  smokeless  powder,  which  is  tough 
and  flexible  and  cannot  be  broken.  It  is  therefore  cut  into 
the  required  form  by  special  machines,  or  pressed,  while  still 
pasty,  through  holes  in  a  die,  thus  forming  strings  or  cords. 

DRYING.— The  sheets  are  cut  while  still  saturated  with 
the  solvent,  and  the  drying  accomplished  after  the  powder 
is  reduced  to  grains. 

This  operation  should  take  place  slowly,  and  at  a  rela- 
tively low  temperature.  Without  this  precaution  there  is 
danger  of  evaporating  the  remaining  solvent  too  rapidly, 
which  would  cause  disintegration  of  the  material  and  in- 
crease the  porosity. 

Smokeless  powders  are  difficult  to  dry,  especially  when 
thick,  and  hence  when  considerable  thickness  is  required,  as 
with  cannon-powder,  several  thin  sheets  previously  dried 
are  placed  on  each  other,  and  the  whole  compressed  to  the 
required  thickness  by  hydraulic  pressure. 

The  drying  should  not  be  complete,  a  certain  quantity  of 
the  solvent  being  left ;  as  in  the  case  of  black  powders,  a 


126  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

certain  quantity  of  moisture  is  retained.     This  tends  to  di- 
minish the  pressure  and  to  keep  up  the  normal  velocity. 

The  great  difficulty  in  the  manufacture  of  smokeless 
powder  has  been  to  make  it  in  large  quantities  by  machinery, 
so  that  it  shall  give  uniform  results  as  to  velocity  and  pressure. 
It  is  not  difficult  to  make  small  quantities  in  a  laboratory, 
but  very  difficult  to  reproduce  them  on  a  large  scale. 

64.  Classification  of  Smokeless  Powders — Classes  1,  2,  and  3 — Wet- 

teren  Powder. 

The  manufacture  described  above  applies  only  to  the 
nitro-cellulose  classes  of  smokeless  powders;  but  as  the 
others  are  generally  mixtures  of  different  substances,  in  the 
state  of  powder,  their  preparation  resembles  that  of  gun- 
powder and  requires  no  special  description. 

CLASSIFICATION.  —  Smokeless  powders  are  generally 
classed  as: 

1.  Those  derived  from  picric  acid  and  the  picrates; 

2.  Those  derived  from  ammonium  nitrate ; 

3.  Those  derived  from  nitro-cotton  or  from  mixtures  of 
nitro-glycerine  and  nitro-cotton,  with  the  addition  of  cer- 
tain agents  which  act  to  modify  the  rate  of  burning. 

Class  i.  Picric-acid  Powders. — Of  these  Designolle's  and 
Brugere's  powders  have  already  been  described.  This  class 
is  no  longer  of  much  importance,  as  it  has  been  abandoned 
for  powders  of  class  3. 

Class  2.  Ammonium-nitrate  Poivders. — The  objection  to 
this  class  of  powders  is  that  they  are  all  highly  hygroscopic, 
and  they  are  no  longer  used. 

Class  3.  There  are  a  few  well-known  powders  of  this  class. 
Very  little  is  known  about  their  actual  composition,  and 
hence  only  a  general  description  of  them  can  be  given. 

WETTEREN  POWDER. — This  is  made  in  Belgium.  It  is 
said  to  be  composed  of  nitro-cotton  dissolved  in  acetic  ether, 
with  the  addition  of  nitrate  of  baryta.  Another  composition 
given  is  nitro-cotton  dissolved  in  acetic  ether,  with  the 
addition  of  nitro-mannite,  which  is  formed  by  the  action  of 
nitric  acid  on  manna-sugar.  The  grains  are  hard,  square  in 
form,  and  of  a  slate  color. 


HIGH  EXPLOSIVES  AND    SMOKELESS   POWDERS.       I2/ 

To  protect  it  irom  moisture  the  grains  are  varnished 
with  a  special  collodion. 

The  defects  of  this  powder  are,  it  is  expensive ;  the  acetic 
ether  does  not  thoroughly  dissolve  the  nitro-cellulose ;  and 
after  the  solvent  is  evaporated,  white  scales  are  formed  on 
the  surface.  In  time  this  powder  loses  its  compact  struc- 
ture, and  under  the  influence  of  shock  reduces  to  dust  in  the 
cartridge-case,  and  this  dust  will  cause  excessive  pressures. 
Also  the  acetic  ether  is  difficult  to  evaporate,  and  hence 
different  parts  of  the  powder  may  contain  different  amounts 
of  the  solvent,  and  this  gives  rise  to  irregular  ballistic  quali- 
ties. This  powder  is  now  being  tried  in  the  U.  8.  cal.  30 
rifle,  charge  37  grains,  muzzle  velocity  2000  ft.-secs. 

65.   Powder  B.  N.  F.—Ballistite— Cordite. 

POWDER  B.  N.  F. — This  powder  is  used  in  France  in  the 
Lebel  rifle.  Its  composition  is  unknown,  but  it  is  supposed  to 
be  a  mixture  of  cottons  of  different  degrees  of  nitration,  gela- 
tinized by  suitable  solvents.  It  is  first  formed  into  plates, 
these  are  rolled  into  sheets,  which  are  cut  up  into  grains  for 
small  arms  or  into  strips  for  large  guns.  It  has  a  grayish  or 
yellowish  color,  is  difficult  to  ignite,  and  is  said  to  be  very 
regular  in  its  action  and  not  affected  by  change  of  climate. 

BALLISTITE. — This  powder  is  used  in  Germany  and  Italy, 
and  is  the  invention  of  Alfred  Nobel.  It  was  the  first  success- 
ful smokeless  powder  made  by  uniting  nitro-glycerine  and 
nitro-cellulose.  By  acting  upon  a  soluble  gun-cotton  with 
nitro-glycerine  in  the  proportions  previously  given,  Nobel 
produced  explosive  gelatine.  By  increasing  the  proportions 
of  the  nitro-cellulose  to  30  or  40  per  cent  and  reducing  the 
nitro-glycerine  to  60  or  70  per  cent,  the  resulting  mixture 
becomes  a  horny  compact  mass  capable  of  definite  granula- 
tion. About  7  per  cent  of  camphor  dissolved  in  the  nitro- 
glycerine is  found  to  assist  the  process.  In  the  manufacture, 
benzole  is  mixed  with  the  nitro-glycerine,  to  render  the 
nitro-celiulose  temporarily  insoluble  in  order  to  facilitate 
its  equal  distribution  and  absorption.  The  benzole  is  then 
evaporated  and  the  material  repeatedly  passed  through 
steam-heated  rolls  and  made  into  sheets.  These  are  after- 


128  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

wards  cut  up  into  cubical  grains  which  are  dark  brown  in 
color  and  are  horny  and  translucent  when  cut.  It  has  about 
three  times  the  ballistic  force  of  black  powder,  and  its  effects 
are  very  regular. 

CORDITE. — This  powder  is  used  in  England  and  is  the 
invention  of  Sir  F.  Abel  and  Professor  Dewar.  It  is  very 
similar  to  ballistite,  except  that  a  highly  nitrated  gun-cotton 
is  used. 

As  this  is  insoluble  in  nitro-glycerine,  to  obtain  a  stable 
union  with  the  latter  it  is  necessary  to  dissolve  the  gun- 
cotton  in  a  solvent.  Acetone  is  used.  Various  slowing 
agents  have  been  tried.  Tannin  is  called  for  in  the  patent, 
but  at  the  present  time  about  10  or  15  per  cent  of  vaseline 
is  preferred. 

These  powders  are  perfectly  smokeless,  and  give  high 
velocities  with  safe  pressures.  They  are  said  to  deteriorate 
rapidly,  the  manufacture  is  dangerous,  and  in  some  samples 
the  nitro-glycerine  exudes,  rendering  the  powder  sensitive. 
They  give  great  heat  on  explosion,  and  this  may,  it  is 
thought,  injuriously  affect  the  bores  of  guns.  They  are  also 
difficult  to  explode. 

66.  Leonard  Powder — Peyton  Powder. 

LEONARD  POWDER. — This  is  an  American  powder  whose 
composition  is  gun-cotton  dissolved  in  acetone,  a  large  per- 
centage of  nitro-glycerine,  and  a  slowing  agent. 

In  shape  it  resembles  cordite  for  large  guns,  the  diam- 
eter of  the  cord  increasing  with  the  calibre  of  the  gun.  For 
small  arms  the  cords  are  very  small,  and  are  cut  in  short 
pieces,  so  that  the  powder  is  granular  in  appearance. 

This  powder  has  given  good  results  in  proof,  and  it  is 
now  undergoing  trial.  The  grains  are  rather  soft. 

PEYTON  POWDER. — This  is  also  an  American  powder, 
manufactured  by  the  California  Powder  Works.  It  is  a 
gelatinized  mixture  of  nitro-glycerine  38  per  cent  and  gun- 
cotton  40  per  cent,  acted  on  by  acetone,  with  certain  other 
substances  added. 

The  mixture  is  incorporated  in  a  small  wheel-mill,  cov- 
ered to  prevent  loss  of  solvent.  After  incorporation  the 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS,       129 

plastic  mass  is  pressed  by  hydraulic  pressure  through  a  hole, 
in  the  centre  of  which  is  a  rod.  This  forms  the  mass  into  a 
hollow  cylinder  or  pipe.  As  the  cylinder  passes  out  of  the 
hole,  it  is  cut  open  longitudinally  by  a  cutter,  and  is  spread 
out  into  a  flat  sheet,  about  10  inches  wide  and  \  inch  thick. 
This  sheet  is  run  through  a  set  of  rollers  with  transverse 
grooves  and  ridges.  By  this  means  the  sheets  are  cut  into 
a  series  of  strips,  but  the  strips  are  not  entirely  separated,  as 
they  are  still  united  by  a  thin  film  of  the  material,  so  that 
the  sheet  can  be  handled  as  a  whole.  These  sheets  are  then 
passed  under  a  cutter,  acting  at  right  angles  to  the  strips, 
by  which  they  are  cut  into  grains.  The  length  and  width 
of  the  grains  are  about  equal.  By  this  operation  most  of 
the  grains  will  be  separated  from  each  other.  Those  that 
stick  are  rubbed  on  a  sieve  or  rolled  in  a  barrel.  The 
grains  are  then  dried  at  a  temperature  of  about  5i°.6C.,  to 
drive  off  the  solvent,  which  is  collected,  and  are  finally 
polished  and  glazed.  The  size  of  the  grain  increases  with 
the  calibre  ol  the  gun,  and  must  be  determined  by  experi- 
ment for  any  particular  gun. 

The  above  particulars  were  furnished  by  Mr.  W.  R. 
Quinan  of  the  California  Powder  Company. 

This  powder  is  also  being  tried  by  the  United  States,  ai 
lot  of  5000  Ibs.  having  been  purchased  for  the  cal.-3O  rifle. 

Mr.  Longridge  gives  the  following  as  the  relative  energies 
in  foot-tons  developed  by  equal  weights  of  the  three  powders 
given  below,  the  energy  of  brown  powder  being  unity: 

Cordite 4-i6 

Ballistite 3-44 

Poudre  B.  N 2.48 

67.  Conditions  to  be  Fulfilled  by  Smokeless  Powders— Smokeless- 
ness— Velocities  and  Pressures— Stability. 
CONDITIONS.— Smokeless  powders  should  fulfil  the  fol- 
lowing conditions : 

1.  They  should  be  approximately  smokeless. 

2.  They  must  give  high  and  uniform  velocities,  with  safe 
and  regular  pressures. 

3.  They  must  be  chemically  and  physically  stable,  under 
varying  conditions  of  moisture,  temperature,  and  age. 


130  TEXl^-BOOK  OF  ORDNANCE  AND    GUNNERY. 

4.  They  must  not  cause  excessive  fouling,  or  excessive 
heating  of  the  gun. 

5.  They  must  not  be  sensitive  to  friction  or  shock. 

6.  The    manufacture  should  not  be  difficult  or  danger- 
ous, or  the  ingredients  very  expensive. 

7.  The  products  of  combustion  should  not  be  noxious, 
and  should  not  corrode  the  gun. 

8.  There  must  be  no  chemical  action  upon  the  cartridge- 
case. 

9.  They  should  give  the  required  ballistic  results  with 
reduced    weight    of    charge,    and    the    charge    should    not 
occupy  a  large  volume,  and  should  be  so  grained  as  to  be 
loaded  in  the  ordinary  loading-machine. 

SMOKELESSNESS. — Nearly  all  the  powders  introduced 
satisfy  this  condition.  Those  of  class  3,  however,  are  the  only 
ones  which  are  in  general  truly  smokeless,  but  the  smoke  from 
the  others  is  rapidly  dissipated.  In  most  of  them  a  slight 
mist  is  visible,  since  the  water  formed  in  the  explosion  is 
condensed  by  the  air,  and  the  priming  or  lubricant  or  the 
slowing  agent  also  produces  visible  smoke. 

VELOCITIES  AND  PRESSURES. — Very  few  of  the  powders 
fulfil  this  condition. 

Experiment  shows  that,  especially  for  small  arms,  a  very 
slight  variation  of  size  of  grain,  weight  of  charge,  or  density 
of  loading  gives  a  great  variation  of  pressure.  For  instance, 
a  variation  of  weight  of  one  grain  in  the  small-calibre  rifle 
increased  the  pressure  from  44,740  to  51,620  Ibs.  per  square 
inch,  while  the  velocity  was  increased  only  88  ft.-secs. 

CHEMICAL  AND  PHYSICAL  STABILITY. — This  is  another 
point  about  which  there  is  great  doubt.  Most  of  these 
powders  are  of  such  recent  date  that  sufficient  time  has  not 
elapsed  to  test  their  stability.  They  are  generally  made  as 
wanted  for  purposes  of  experiment,  and  used  in  a  short  time. 
Tests  are  being  made,  however,  upon  this  subject  by  all 
countries. 

Cordite  has  been  tested  as  to  changes  of  climate  in  India 
and  Canada  with  good  results. 

Ballistite  has  been  soaked  in  water,  dried  and  fired,  with 
very  little  change  in  ballistic  qualities. 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS.       13! 

68.  Fouling  —  Sensitiveness  —  Safety  and  Cost  of  Manufacture  — 
Character  of  Products  of  Explosion  —  Chemical  Action  — 
Weight  of  Charge  and  Specific  Gravity. 

FOULING. — As  a  rule  there  is  very  little  fouling  with 
smokeless  powders.  The  fact  that  they  are  smokeless  in- 
dicates at  once  the  absence  of  the  residue  of  solid  particles 
which  causes  fouling  with  ordinary  black  powders.  This 
absence  of  fouling,  however,  has  proved  to  be  a  disadvantage 
in  small  arms,  owing  to  the  increased  friction  between  the 
bullet  and  the  bore,  which  the  fouling  prevented,  by  acting 
as  a  lubricant.  This  friction  has  sometimes  been  so  great  as 
to  strip  the  covering  off  the  bullet  and  leave  it  in  the  bore. 

Various  lubricants  have  been  tried  to  overcome  this 
defect,  but  none  of  them  have  proved  satisfactory,  and  the 
defect  has  been  overcome  by  using  a  proper  covering  for 
the  bullet,  either  of  copper,  nickled  steel,  or  German  silver. 

SENSITIVENESS. — All  the  powders  are  safe  in  this  respect, 
and  have  been  pretty  thoroughly  tested.  The  difficulty  lies 
in  the  opposite  direction,  as  they  are  so  insensitive  that  they 
are  difficult  to  explode,  and  for  most  of  them,  special  primers, 
or  more  powerful  ones,  are  required. 

Nitro-cellulose  powders  are  specially  insensitive. 

SAFETY  AND  COST  OF  MANUFACTURE. — The  principal 
danger  arises  in  the  manufacture  of  the  ingredients,  nitro-gly- 
cerine  and  gun-cotton,  and  in  handling  the  former.  While 
explosions  sometimes  occur,  the  manufacture  can  hardly  be 
considered  more  dangerous  than  that  of  gunpowder.  The 
question  of  cost  is  subordinate  to  that  of  efficiency,  and 
would  only  enter  in  deciding  between  two  or  more  powders 
of  equally  good  ballistic  properties. 

CHARACTER  OF  PRODUCTS.— The  character  of  the  gaseous 
products  differs  very  little  from  those  of  gunpowder,  being 
principally  CO,  CO.",  H2O,  and  N,  and  hence  no  danger  is  to 
be  apprehended  from  them,  and  they  should  not  corrode  the 
gun.  Corrosive  effects  have  been  noticed,  but  they  are  due 
to  the  great  heat  of  the  gases. 

CHEMICAL  ACTION.— So  far  as  is  known,  these  powders 
do  not  act  chemically  upon  the  cartridge-cases. 

WEIGHT  OF  CHARGE  AND  SPECIFIC  GRAVITY.— These 


132  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

powders  have  much  higher  ballistic  qualities  than  the  old 
nitrate  powders,  and  hence  a  much  smaller  charge  will  give 
greater  velocities.  The  weight  of  the  charge,  for  the  .30- 
cal.  rifle  is  37  grains,  and  that  of  the  projectile  220  grains. 
That  of  the  old  cal.-45  rifle  was,  powder  70  grains,  bullet 
500  grains. 

This  reduction  in  weight  of  cartridge  has  an  important 
bearing  upon  the  number  of  rounds  carried  by  the  soldier. 
It  is  evident  that  with  a  magazine  arm  the  number  of  car- 
tridges used  will  be  greatly  increased,  and  the  reduction 
in  weight  enables  them  to  be  carried  with  ease. 

The  specific  gravity  and  gravimetric  density  of  the  new 
powders  are  less  than  those  of  the  old,  and  hence  they  oc- 
cupy a  greater  volume  for  the  same  weight ;  but  as  the 
weight  necessary  to  give  the  same  or  better  results  is  less 
for  each  charge,  the  decrease  in  density  occasions  no  diffi- 
culty. 

69.  Cause  of  Ballistic  Superiority  of  Smokeless  Powders. 

The  superior  effects  of  the  smokeless  powders  may  be 
explained  by  considering  their  potential,  force,  and  rapidity 
of  reaction. 

1.  Potential. — This  is  much  greater  than  with  the  old  ni- 
trate powders,  as  the  quantity  of  heat  evolved  in  the  com- 
bustion   of   gun-cotton   and   nitro-glycerine   is   very    much 
greater  than  that  of  ordinary  powder.     This  heat  measures 
the  quantity  of  work  which  the  gases  can  do  upon  the  pro- 
jectile, and  hence  the  energy  of  the  latter  is  much  greater, 
and  we  have  higher  velocities. 

2.  Force. — This  is  also  greater  than  with  the  old  powders, 
as  the  specific  volume  of  the  gases  and  their  temperature 
are  higher. 

The  specific  volume  is  greater  because  all  the  powder  is 
converted  into  gas.  This  force  tends  to  increase  the  press- 
ure exerted  by  the  gases  upon  the  gun  at  the  origin,  and 
hence  this  pressure  would  be  very  great  if  it  were  not 
that— 

3.  The  Rapidity  of  Reaction  is  very  much  decreased,  so 
that  the  gas  is  given  off  slowlv,  and  allows  the  projectile 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS.       133 

to  start  from  its  original  position  before  this  pressure  has 
reached  too  great  a  value. 

These  powders  burn  very  slowly  in  air,  but,  like  the  ni- 
trate powders,  their  rate  of  burning  increases  very  rapidly 
with  the  pressure,  and  probably  if  this  pressure  were  very 
high  they  would  detonate. 

Another  circumstance  concurs  to  prevent  this,  however, 
and  that  is  that  the  powder  has  no  solid  residue,  and  hence 
all  the  space  in  the  powder-chamber  and  in  rear  of  the  pro- 
jectile is  occupied  by  the  gas.  In  ordinary  powders  about 
.57  of  this  space,  or  more  than  half,  is  occupied  by  solid 
residue.  Hence  the  pressure  is  kept  down  at  first,  and, 
owing  to  the  high  temperature  and  great  volume  of  the  gas, 
it  is  maintained  better  along  the  bore  than  with  the  old 
powders. 

We  have  therefore  in  the  new  powders  a  propelling 
agent  which  for  less  weight  gives  safe  pressure  at  first, 
more  gas,  more  heat,  and  more  sustained  pressure  than  the 
old  powders,  and  hence  their  ballistic  superiority. 

TABLE    OF    HIGH    EXPLOSIVES    AND   SMOKELESS 
POWDERS. 

(From  Cundill's  "  Dictionary  of  Explosives.") 

I.  NITRATE  MIXTURES. 

NAME.  COMPOSITION. 

f  Nitre,  101  parts 

Amide  Powder •]  Ammonium  nitrate,        80 

(  Charcoal,  4°     " 

II.  CHLORATE  MIXTURES. 

,  j  Chlorate  potash,  3  parts 

1  Mono-nitro-benzine,         i  part 

III.  NITRO  COMPOUNDS. 

j  Gun-cotton 
Abel's  Glyoxiline j  Nitro.glycerine 

i  Gun-cotton 

Also    <  Potassium  nitrate 
(  Nitro-glycerine 


134  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY, 

(  Nitro-glycerine,  15  to  65  parts 
JEtna.  Powder  .............    -j  Sodium  nitrate 

f  Wood-pulp 

f  Sodium  nitrate,  2  parts 

Wood  fibre,  21     " 
Magnesium   carbonate,    2 

Nitro-glycerine  75     " 

Ammonium  nitrate         8^     " 
.  _  ,     . 
Tn-mtro-benzme  17 

Blasting  Gelatine  ..........    Di-nttro-cellulose   dissolved    in    nitro- 

glycerine 
Borland  Powder   }  j  Nitro-glycerine,  90  parts 


( 
Belhte  ...................    1. 

( 


I Ic" 


Carbo-dynamite    )  (  Charcoal,  10 

(  Nitro-glycerine,  so     " 

Dittmar  Powder   )  \  * 

..  [• 4  Sawdust,  30 

Dualme  j  J  _ 

I  Potassium  nitrate  20 

Dynamite  No.  i \  Nitro-glycerine,  75 

(  Kieselguhr,  25     " 

Giant  Powder (See  Dynamite.) 

Judson  Powder Gunpowder  coated  with  mtro-glycerine 

Lithofracteur (See  Rendrock.) 

(  Sugar  of  manna 
Nitro-mannite J  Nitric  acid 

(  Sulphuric  acid 

f  Potassium  nitrate,  40  parts 

Rendrock J  Nitro-glycerine,  40     " 

|  Wood-fibre,  13 

t  Paraffine,  7     " 

Ammonium  nitrate 
Chlorinated  di-nitro-benzine 

(  Nitro-lignin 

I  Potassium  nitrate 

Shultze  Powder <{  Barium  nitrate 

(a  sporting  powder)  Sawdust 

I  Paramne 

„,     .  (  Gun-cotton 

Tonite }  , 

/u .  ,     x  {  Barium  nitrate 

(blasting-powder) 

IV.  PICRIC  POWDERS. 

(  Ammonium  picrate,        ^4  parts 
Brugere  s  Powder .  * 

(  Potassium  nitrate,  46 


(  j± 
Roburite ' -j 

(  v^l 


HIGH  EXPLOSIVES  AND    SMOKELESS  POWDERS,        135 

(  Potassium  picrate,  9  parts. 

Designolle's  Powder •<  Potassium  nitrate,  80     " 

(  Charcoal,  n     " 

(  Gun-cotton  dissolved  in  ether 
Melinite I  Picric  acid 

(  Cresylic  acid 

V.  SPRENGEL  MIXTURES. 

(  Di-nitro-benzine 

Hellhoffite ]  XT.    . 

(  Nitric  acid 

Rack-a-rock (See  ante.) 


VI.  MISCELLANEOUS. 

(  Chlorate  potash 
Caps  for  Toy  Pistols  . . . .    j  A         houg  phosphorus 

f  Fulminate  mercury,          6  parts 
j  Potassium  chlorate,          6     " 
Percussion-caps <j  Antimony  suiphide,         4 

[  Ground  glass,  2 

•\  f  Mercury 

Mercury     f  )  Nitric  acid 

Fulminate  J  '  (  Akohol 

c  Tin  cases  filled  with  powder  and  hav- 

Railroad  Fog-signals ]          ing  cones  with  ordinary  percus- 

(          sion-caps. 


CHAPTER   III. 

GUNS. 

GUN-STEEL. 

70.  Definition  of  Gun-steel— Chemical  Composition— Different  Con- 
stituents and  their  Effect. 

DEFINITION.— Steel  is  an  alloy  of  iron  and  carbon,  the 
percentage  of  the  latter  being  from  o.io  to  2.5.  This  per- 
centage, however,  does  not  always  serve  to  classify  steel,  as 
it  runs  into  wrought  iron  on  the  one  hand,  and  into  cast-iron 
on  the  other.  It  is  distinguished  from  cast  iron  by  its 
quality  of  becoming  hard  when  heated  to  a  certain  tern- 
perature  and  cooled  quickly,  and  of  having  this  hardness 
reduced  by  a  process  called  tempering. 

It  is  distinguished  from  wrought  iron  by  this  same  qual- 
ity, and  also  by  being  cast  into  molds  or  ingots,  which  is  not 
possible  with  wrought  iron,  the  latter  not  being  fluid  except 
at  very  high  temperatures.  In  gun-steel  the  proportion  of 
carbon  is  low,  not  exceeding  0.5  per  cent  as  a  rule. 

CHEMICAL  COMPOSITION. — Upon  this  point  there  is  great 
difference  of  opinion.  Steel  is  called  an  alloy  of  iron  and 
carbon,  but  the  exact  condition  of  the  carbon  is  not  known. 

It  is  sometimes  called  dissolved  carbon  for  the  harder 
steels,  and  undissolved  for  the  softer;  also  "hardening" 
and  "  cement "  carbon,  for  the  harder  and  softer  steels  re- 
spectively. More  recently  it  is  called  "  fixed  "  carbon  for 
the  hard,  and  "  free"  carbon  for  the  soft  steels.  These  two 
carbons  may  be  changed  from  the  one  to  the  other,  as  the 
result  of  special  treatment. 

OTHER  CONSTITUENTS. — Besides  the  carbon,  there  are 
always  other  substances  present,  some  of  which  are  bene- 

136 


GUNS.  !37 

ficial  and  others  injurious  to  its  quality.     Among  the  prin- 
cipal of  these  substances  are  : 

1.  Sulphur. — This  is  injurious  to  the  steel,  as  it  makes  it 
difficult  to  forge,  producing  "  hot-shortness,"  or  brittleness 
when  hot. 

2.  Phosphorus. — This  is  also  injurious,  as  it  has  the  effect 
of  making  steel  brittle  when  cold,  or  "  cold-short." 

3.  Manganese. — This  when  added  in  proper  proportions 
improves  the  quality  of   the  steel,  rendering   it   hard  and 
tough. 

4.  Silicon. — Is  valuable,  as  it  forms  a  fusible  slag  with  the 
iron  oxide  in  manufacture,  and  prevents  the  formation  of 
gas,  and  consequently  of  blow  holes  in  the  steel.     If  in  too 
great  quantity,  it  causes  brittleness. 

5.  Chromium. — Gives    great   hardness   to   steel  without 
brittleness,  and  hence  the  best  forged  steel  projectiles  are 
made  of  chrome-steel. 

6.  Nickel. — This  gives  great  toughness  to  steel,  so. that 
armor-plates  made  of  nickel-steel  resist  racking  very  well. 

Nickel-steel  is  also  being  experimented  with  for  guns,  at 
present. 

71.  Physical  Qualities  —  Hardness  —  Toughness  —  Elastic  Limit— 
Hooke's  Law— Tensile  Strength. 

HARDNESS.— Gun-steel  should  be  sufficiently  hard  to  re- 
sist deformation  from  blows,  and  also  the  action  of  the  pro- 
jectile and  the  powder-gases;  but  hardness  is  generally 
accompanied  by  an  undesirable  quality,  brittleness,  and 
hence  a  modification  called  toughness  is  sought  in  this  metal. 

TOUGHNESS  is  the  quality  which  enables  a  metal  to  under- 
go considerable  change  of  form  under  the  action  of  a  force, 
without  rupture,  and  with  great  resistance  to  that  change. 

ELASTICITY  AND  ELASTIC  LIMIT.— When  a  tensile  stress 
or  force  is  applied  to  a  piece  of  steel,  it  will  elongate  a  cer- 
tain amount. 

This  total  elongation,  divided  by  the  original  length,  wil 
give  the  elongation  per  unit  of  length.     When  the  stress  or 
force  ceases  to  act,  the  steel  will  recover  its  original  length, 
provided  the  stress  is  not  too  great.     If  an  additional  force 


138  TEXT- BOOK  OF  ORDNANCE  AND    GUNNERY. 

be  applied,  a  similar  effect  will  be  obtained,  the  elongation 
per  unit  of  length  being  greater  in  this  case,  and  the  metal 
returning  again  to  its  original  length  when  the  stress  ceases 
to  act.  The  same  effects  will  be  observed  till  the  stress 
reaches  a  certain  amount,  when  the  metal  will  not  return  to 
its  original  length,  but  will  acquire  a  permanent  set.  If  the 
stress  next  below  the  one  which  produces  the  permanent  set 
be  measured,  and  be  divided  by  the  area  of  cross-section  of 
the  metal,  it  will  give  the  elastic  limit  of  the  metal ;  and  if  the 
elastic  limit  be  divided  by  the  corresponding  elongation  per 
unit  of  length,  the  result  will  be  the  modulus  or  coefficient 
of  elasticity  of  the  metal. 

Let  a  be  the  area  of  cross-section  of  the  metal ; 

/,  its  length ; 

K,  the  total  elongation ; 

W,  the  stress  acting  at  the  elastic  limit ; 

£,  the  modulus  of  elasticity  ; 

0,  the  elastic  limit. 

Then 

?=?= 


F  -  JL 

~~  K  ~~        ' 


Denoting  by  A  the  elongation  per  unit  length,  we  have 


and 


HOOKE'S  LAW. — The  ratio  of  stress  to  elongation  remains 
constant  up  to  the  elastic  limit,  and  this  constant  ratio  is  the 
modulus  of  elasticity  E.  This  is  expressed  as  follows : 


GUNS. 

Within  *the  elastic  limit  of  a  metal,  the  stress  is  proper- 
tional  to  the  strain.  This  is  called  Hooke's  law. 

If  we  compare  two  kinds  of  steel,  one  having  a  high  per- 
centage  ol  carbon,  and  the  other  a  low  percentage,  it  will 
be  found  that  the  steel  high  in  carbon  has  a  high  elastic 
limit,  and  that  low  in  carbon  a  low  limit.  Since  the  modulus 
of  elasticity  for  all  steel  is  nearly  constant,  and  equal  to 
about  30,000,000  Ibs.  per  square  inch,  the  high  steel  will 
elongate  more  at  the  elastic  limit  than  the  low  (equation 
169)).  From  this  alone  it  would  appear  that  the  high  steel 
is  best  for  gun-construction,  since  it  enables  the  metal  to 
yield  more  to  the  stresses  of  the  powder-gas,  and  to  recover 
its  original  form  without  permanent  set. 

The  reason  why  high  or  hard  steel  is  not  used  is,  that  it. 
is  liable  to  flaws,  strains,  or  incipient  cracks,  produced  in 
manufacture,  especially  in  large  pieces.  A  hard  steel  is 
also  dangerous,  because  after  passing  its  elastic  limit,  it  has 
very  little  remaining  strength,  and  breaks  easily,  and  with 
little  warning,  while  the  soft  steel  yields  considerably  with- 
out fracture,  after  passing  the  elastic  limit,  exhibiting  the 
quality  of  toughness,  previously  defined. 

TENSILE  STRENGTH.— By  this  is  commonly  understood 
the  stress  per  unit  area  required  to  rupture  the  metal.  It  is 
not  of  great  importance  in  gun-steel,  although  limits  are 
prescribed  for  it  in  the  tests,  since  we  consider  the  elastic 
limit  only  in  gun-construction. 

For  clearness,  a  tensile  stress  only  has  been  considered. 

The  same  relations  hold,  however,  for  compression  or 
torsional  stress,  and  each  has  its  corresponding  elastic  limit 
and  modulus. 

72.  Structure  of  Steel— Defects— Blow-holes— Pipes. 

STRUCTURE.— Steel  is  always  a  crystalline  metal,  and  has 
no  fibrous  structure  like  wrought  iron.  These  crystals  are 
generally  small,  and  vary  in  size  and  appearance  with  the 
treatment  the  metal  receives  after  casting.  They  are  very 
small  in  the  best  steels,  and  may  be  so  small  that  the  frac- 
ture will  lose  its  crystalline  appearance. 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

DEFECTS. — These  are  common  to  all  cast  metals,  and 
•steel  has  some  in  addition  peculiar  to  itself. 

Slow  Cooling  in  large  masses  gives  large  crystals,  and 
consequently  a  weak  steel.  It  also  causes  a  lack  of  uni- 
formity in  the  steel.  This  being  an  alloy  of  iron  and  car- 
bon, and  the  carbon  being  combined  in  different  proportions 
throughout  the  fluid  mass,  the  alloys  highest  in  carbon  are 
the  lightest,  and  will  rise  to  the  top.  Hence  the  hardest 
steel  is  found  here.  For  the  same  reason,  the  softest  will 
be  at  the  bottom  of  the  ingot.  The  middle  portion  of  the 
length  will  therefore  give  the  best  steel.  As  the  fusibility 
of  the  steel  increases  with  the  percentage  of  carbon,  those 
portions  low  in  carbon  will  solidify  first,  and  hence,  in  the 
same  cross-section,  the  part  high  in  carbon  will  be  near  the 
centre,  where  the  mass  remains  fluid  longer. 

BLOW-HOLES. — This  defect  is  peculiar  to  steel,  and  is  due 
to  the  gases  in  the  melted  metal,  which,  being  unable  to  es- 
cape, are  imprisoned  in  the  casting,  and  form  holes.  These 
blow-holes  are  causes  of  weakness  in  steel,  as  it  is  impossible 
to  discover  them,  and  forging  or  compression  only  changes 
their  form,  but  does  not  remove  them.  Various  theories 
have  been  advanced  to  account  for  their  presence,  and  at- 
tempts made  to  get  rid  of  them.  They  are  more  prevalent 
in  the  Bessemer  than  in  the  open-hearth  steels,  by  which 
latter  process  gun-steel  is  made. 

The  lower  the  temperature  at  which  the  steel  is  cast,  the 
more  apt  are  these  blow-holes  to  occur,  because  the  metal 
hardens  before  the  gas  has  time  to  escape. 

PIPES. — These  are  cavities  formed  in  the  axis  of  the 
ingot,  due  to  internal  strains  from  cooling.  They  generally 
occur  when  the  metal  is  cast  too  hot.  Thus  on  the  one 
hand  too  low  a  temperature  causes  blow-holes,  and  too  high 
a  temperature  pipes. 

To  avoid  these  defects  in  gun-steel,  6  per  cent  of  the 
total  weight  of  the  cast  ingot  is  cut  from  the  bottom  and 
33^  per  cent  from  the  top,  the  remainder  being  used  for  the 
lorging.  The  piping  and  weak  metal  in  the  centre  of  the 
ingot  are  removed  by  boring  or  cutting  out  the  central  part 
of  the  ingot.  Blow-holes  can  be  prevented  only  by  careful 


GUNS. 


141 


treatment  in  casting,  arid  their  presence  cannot  be  detected 
except  by  subsequent  working,  and  not  then  if  they  are 
beyond  the  reach  of  the  tools  employed. 

73.  Working  Qualities  of  Steel  —  Fusibility  —  Malleability  and 
Ductility — Welding — Annealing. 

FUSIBILITY.— This  quality  enables  steel  to  be  cast  into 
various  shapes,  and  into  ingots  for  gun-forgings.  It  re- 
quires, however,  a  relatively  high  temperature,  and  has 
caused  the  introduction  of  various  special  processes  for 
obtaining  this  temperature.  In  the  Bessemer  process,  the 
heat  necessary  is  obtained,  by  blowing  air  through  a  melted 
mass  of  cast  iron,  by  which  the  carbon  and  silicon  are  oxi- 
dized, and  a  high  temperature  produced.  In  the  open- 
hearth  process,  the  high  temperature  is  ootamed  by  the  use 
of  gaseous  fuel,  and  by  storing  up  the  waste  heat  of  the  fur- 
nace in  chambers  of  fire-brick,  through  which  the  gaseous 
fuel  passes,  and  by  which  it  is  raised  to  a  high  temperature. 

MALLEABILITY  AND  DUCTILITY.— Steel,  when  heated  to 
a  red  heat,  possesses  the  property  of  malleability,  and  it  is 
due  to  this  fact  that  it  can  be  forged  into  any  shape.  When 
cold,  owing  to  its  ductility,  it  can  be  drawn  into  wire,  which 
is  used  in  wire  guns  and  for  various  other  purposes. 

WELDING. — Ordinarily  steel  cannot  be  welded  except 
when  very  low  in  carbon,  and  approaching  wrought  iron. 
Lately,  however,  the  process  of  electric  welding  has  been 
introduced,  and  by  it  the  welding  can  be  readily  accom- 
plished. 

ANNEALING  —This  is  a  very  valuable  property  possessed 
by  steel.  By  heating  it  to  a  certain  temperature  and  allow- 
ing it  to  cool  slowly,  a  piece  of  hard  steel  will  become  soft, 
so  that  it  can  be  readily  worked  in  the  lathe.  After  work- 
ing, it  can  be  returned  to  its  former  hard  condition,  by 
heating  it  again,  and  cooling  it  quickly.  After  forging  or 
working  steel,  it  generally  has  internal  strains  due  to  these 
processes,  and' these  strains  may  be  removed  by  annealing. 
By  cooling  in  oil,  the  tensile  strength  and  elastic  limit  of 
steel  are  greatly  increased,  and  these  qualities,  especially 
elasticity,  are  very  valuable  in  gun-construction. 


142 


TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 


74.  Manufacture  of  Gun-steel — Open-hearth  Process — Gas-producer 
and  Regenerators. 

OPEN-HEARTH  PROCESS. — All  gun-steel  at  the  present 
day  is  made  by  this  process,  which  derives  its  name  from  the 
fact  that  the  receptacle  in  which  the  steel  is  melted  is  open 
at  the  top,  and  exposed  to  the  flame  of  the  fuel  which  plays 
over  the  surface,  and  performs  a  principal  part  in  the  forma- 
tion  of  the  steel.  It  is  also  called  Siemens  or  Siemens-Martin 
steel,  according  to  the  ingredients  used  to  form  the  steel. 

APPARATUS. — The  furnace  used  is  that  invented  by  Dr. 
Siemens,  and  a  general  description  of  it  is  given.  It  con- 
consists  of  the  following  essential  parts  : 

1.  The  gas-producer ; 

2.  The  regenerators ; 

3.  The  furnace  proper. 

THE  GAS-PRODUCER. — The  fuel  used  in  the  Siemens  fur- 
nace is  gaseous,  and  is  obtained  from  ordinary  fuel,  by  sub- 
jecting the  latter  to  a  preliminary  process  in  the  gas-produ- 
cer. This  apparatus,  Fig.  29,  consists  of  a  rectangular 


FIG.  29. 

chamber  of  fire-brick,  one  side,  B,  being  inclined  at  an  angle 
ol  45°  to  60°.  A  is  the  grate.  The  fuel,  which  may  be  of 
any  kind,  is  fed  into  the  producer  through  the  hopper  C. 
As  the  fuel  slowly  burns,  the  CO2  rises  through  the  mass 
above  it,  and  absorbs  an  additional  portion  of  C,  becoming 
converted  into  2CO.  This  gas  passes  out  of  the  opening  D, 
into  a  flue.  In  order  to  cause  it  to  flow  towards  the  furnace, 
it  is  led  through  a  long  pipe,  E,  where  it  is  partially  cooled, 


G  UNS. 


143 


and  it  then  descends  the  pipe  /Heading  to  the  furnace.  The 
gas  in  F  being  cooler  than  that  in  E  and  D,  a  constant  flow 
of  gas  from  producer  to  furnace  is  maintained. 

THE  REGENERATORS.— The  gas  entering  the  furnace  is,  as 
has  been  stated,  CO.  To  burn  it  to  CO2,  air  must  be  mixed 
with  it.  This  mixture  is  made  in  the  furnace  proper,  the 
CO  and  air  being  kept  separate  till  they  reach  the  point 
where  they  are  to  burn.  The  CO  is  cooled  to  some  extent, 
as  shown,  before  being  admitted  to  the  furnace. 

To  heat  both  air  and  CO  before  they  are  mixed  and 
burned,  and  to  accomplish  this  economically,  and  raise  them 
to  a  high  temperature,  the  waste  heat  of  the  furnace  is  em- 
ployed. This  is  the  object  of  the  regenerators,  Fig.  30. 


They  consist  of  four  large  chambers  below  the  furnace, 
tilled  with  fire-brick,  piled  so  that  there  are  intervals  be- 
tween the  bricks  to  allow  the  gas  and  air  to  pass  through. 
Their  action  is  as  follows  :  When  the  furnace  is  started, 
CO  is  admitted  through  A  and  air  through  B,  both  A  and 
B  being  cold.  These  pass  up  through  the  fire-bricks  in  A 
and  B  and  through  flues  at  the  top,  and  flow  into  the  fur- 
nace proper,  where  they  are  lighted.  The  products  of 
combustion  are  caused  to  pass  through  C  and  D,  which  are 
similar  chambers.  In  doing  so  these  products  heat  the  fire- 
bricks in  C  and  D.  After  some  time,— about  one  hour  gen- 
erally,—by  the  action  of  valves  controlled  by  the  workmen, 
the  CO  and  air  are  caused  to  enter  the  furnace  through  C 


144 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY, 


and  D  respectively,  and  the  products  of  combustion  to  pass 
out  through  A  and  B.  In  this  case  the  CO  and  air  entering 
the  heated  chambers  C  and  D  are  raised  to  a  high  tempera 
ture  before  ignition,  and  the  temperature  of  the  furnace 
thereby  greatly  increased.  It  is  also  evident  that  A  and  B 
will  be  more  highly  heated  than  C  and  D  were,  and  hence 
when  the  next  change  is  made  the  gas  and  air  passing 
through  A  and  B  will  be  more  highly  heated  than  when 
passing  through  C  and  D,  and  so  on. 

The  action  of  the  furnace  is  therefore  cumulative,  and 
its  only  limit  in  temperature  is  the  refractoriness  of  the 
material.  By  regulating  the  proportions  of  gas  and  air, 
which  is  readily  done,  the  temperature  may  be  kept  con- 
stant. 

75.  Manufacture  of  Steel  —  The  Furnace  —  Operation  —  Crucible 

Process. 

THE  FURNACE. — The  furnace  proper  consists  (see  Fig. 
31)  of  a  dish-shaped  vessel  D  of  cast  iron,  supported  so  that 


FIG.  31. 

the  air  can  circulate  freely  around  it  and  keep  it  from  melt- 
ing. This  is  lined  with  refractory  sand  S;  and  in  order  to 
repair  it  when  necessary,  the  pan  D  is  generally  arranged  so 
that  it  can  be  run  out  of  the  furnace.  This  allows  it  to  cool 
quickly.  The  pan  is  placed  over  the  regenerators,  and  the 
gaseous  fuel  and  air  enter  by  the  flues  F,  and  the  products 
of  combustion  escape  by  the  flues  JF',  or  the  reverse,  ac- 
cording to  the  position  of  the  regulating-valves. 

The  arrows  show  the  direction  of  these  currents.     The 


GUNS.  145 

roof  R  is  lined  with  fire-brick,  and  by  its  shape  deflects  the 
flame  over  the  metal  in  the  hearth.  At  opposite  ends  of 
the  furnace  are  a  charging-door  for  admission  of  the  metal,, 
and  a  tap-hole  for  drawing  off  the  finished  steel.  These  are 
not  shown  in  the  drawing. 

OPERATION. — The  principle  of  the  process  is  that  when 
wrought-iron  or  steel  scrap  is  added  to  melted  cast  iron,  the 
percentage  of  carbon  is  thereby  reduced  till  it  reaches  that 
required  for  steel.  The  charge  consists  of  pig-iron  heated 
red-hot  in  a  separate  furnace,  and  then  placed  on  the  hearth 
of  the  Siemens  furnace.  By  the  action  of  the  furnace  this 
pig-iron  is  soon  melted.  Scrap  wrought  iron  or  steel  is  then 
added  in  suitable  proportions,  till  the  percentage  of  carbon 
is  low.  When  it  has  reached  the  proper  point,  the  percent- 
age is  made  exact  by  adding  a  pig  iron  containing  a  known 
percentage  of  carbon,  such  as  Spiegeleisen  or  ferro-manga- 
nese,  or  by  the  addition  of  ore.  The  percentage  of  carbon 
is  judged  of  during  the  process  by  taking  samples  from 
the  melted  metal,  cooling  them,  observing  their  fracture 
on  breaking,  and  by  dissolving  portions  of  the  specimen  in 
HNO3  and  comparing  the  color  with  that  of  standard  solu- 
tions of  steel  in  HNO3  containing  different  percentages  o£ 
carbon.  In  this  way  the  composition  of  the  steel  can  be 
exactly  regulated,  as  the  metal  can  be  kept  in  a  melted 
state  without  damage  for  a  considerable  time,  and  the  char- 
acter of  the  flame  made  oxidizing  or  reducing  at  will,  ac- 
cording to  the  relative  amounts  of  air  and  CO  admitted. 

The  operation  ordinarily  lasts  about  eight  hours  for 
each  charge. 

When  the  steel  has  attained  its  proper  composition,  the 
furnace  is  tapped  and  the  metal  cast  into  ingots,  ready  for 
the  succeeding  operations. 

CRUCIBLE  PROCESS.— This  is  used  by  Krupp.  The  in- 
gredients of  the  steel  are  melted  in  crucibles,  and  the  result- 
ing steel  from  the  crucibles  is  poured  into  a  common  reser- 
voir from  which  the  ingots  are  cast. 

The  Bessemer  process,  though  important  and  producing 
large  quantities  of  steel,  is  not  as  yet  used  in  making, 
steel. 


146 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


76.  Casting    Ingots — Ladle — Crane — Ingot-mold — Pouring  —  Sink- 
ing Head. 

After  the  proper  percentage  of  carbon  is  obtained,  the 
steel  is  cast  in  ingots. 

LADLE. — The  first  step  is  to  tap  the  furnace  and  draw 
off  the  steel  into  a  ladle.  This  ladle  is  made  of  boiler-iron 
lined  with  refractory  sand.  It  has  two  trunnions  on  the 
exterior  which  support  it,  and  around  which  it  revolves 

when  tipped,  to  pour  the  metal  into 
the  mold ;  or  it  may  have  a  tap- 
hole  at  the  bottom  closed  with  a 
plug  of  fire-clay,  which  is  lifted  by 
an  iron  rod  covered  with  refractory 
material. 

In  Fig.  32,  T  is  the  tap-hole,  T 
the  trunnions,  R  the  rod,  and  S  its 
casing.     The  advantage  of   tipping 
is  that  it  is  quicker,  and  of  the  tap- 
hole,  that  it  gets  rid  of  scoria  and  impurities  on  the  surface 
of  the  melted  steel,  and  keeps  them  out  of  the  mold. 

CRANE. — This  is  used  to  convey  the  ladle  to  the  molds, 
or,  more  generally,  for  handling  the  ingots  and  molds 
after  the  casting.  It  is  very 
often  found  more  convenient 
to  run  the  ingot-molds  on 
cars  under  the  ladle,  or  under  a 
spout  attached  to  the  furnace. 
INGOT-MOLDS.  —  These  are 
generally  made  of  cast  iron, 
and  are  circular  in  cross-sec- 
tion, to  insure  uniform  cooling. 
They  are  in  one  piece,  and 
slightly  conical  on  the  inte- 
rior, so  that  the  ingot,  after 
casting,  may  be  readily  with- 
drawn. They  may  also  be 
made  in  halves,  parting  on 
an  axial  plane  ;  but  in  this 
case  they  are  liable  to  open  at  the  joint,  due  to  warping. 


J0L 


J0L 


SOLID. 


SPLIT. 


G  UNS. 


'47 


The  interior  surface  is  protected  by  a  wash  of  clay  or 
plumbago.  Melted  steel  poured  into  an  ingot-mold  will 
not  adhere  to  the  sides,  while  melted  cast  iron  will  adhere. 
The  reason  is  that  the  steel  chills  and  contracts  away 
from  the  mold,  while  the  iron  cools  more  slowly  and  fuses 
the  mold.  The  general  shape  of  the  ingot-molds  is  shown 
in  Fig.  33. 

POURING. — If  the  steel  is  very  hot,  it  must  be  poured 
slowly  into  the  molds  in  a  thin  stream.  This  allows  the 
gases  time  to  escape.  If  at  a  lower  temperature,  it  may  be 
poured  more  quickly. 

The  ingot-molds  may  be  warmed  before  casting  to  pre- 
vent undue  cooling  and  consequent  strains,  and  also  the 
formation  of  pipes. 

After  the  steel  is  cast,  the  molds  must  be  covered  to  ex- 
clude air  and  cause  slow  cooling. 

SINKING-HEAD. — In  all  castings,  whether  of  iron,  steel,  or 
other  metal,  an  excess  of  metal,  called  the  sinking-head,  is 
left  at  the  top  of  the  mold.  This  column  of  metal  acts  by 
its  weight  to  give  greater  density  to  the  lower  portions  of 
the  ingot ;  it  also  serves  to  collect  the  scoria  and  impurities 
which  rise  to  the  top,  and  it  fills  any  cracks  or  cavities  that 
may  form  in  the  cooling  of  the  ingot.  It  is  necessary  to 
keep  this  sinking-head  fluid  as  long  as  possible,  and  hence 
it  is  generally  cast  in  a  sand-mold  for  gun-ingots. 

77.  Whitworth's  Process  of  Fluid  Compression. 

Thi^  process  was  invented  by  Sir  Joseph  Whitworth  of 
England,  and  gives  by  hydraulic  pressure,  the  same  effect 
as  that  due  to  the  sinking-head.  It  may  be  regarded  as  an 
artificial  sinking-head  of  great  height.  The  process  con- 
sists in  forcing  the  piston  of  a  hydraulic  ram  down  upon 
the  melted  steel  in  the  mold,  and  maintaining  the  pressure 
till  the  steel  solidifies.  The  ingot-mold  used  in  this  process 
must  be  very  strong  to  withstand  the  great  pressure,  and  it 
has  a  peculiar  arrangement  by  which  the  gases  driven  out 
by  the  pressure  are  allowed  to  escape.  Fig.  34  gives  the 
general  arrangement. 

The   mold  consists  of  a  strong   cast-steel   cylinder,  A, 


148 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


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with  its  bottom',  B.  This  cylinder  is  lined  with  rectangular 
bars  of  wrought  iron,  C,  which  have 
grooves,  D,  cut  at  intervals  along  their 
faces  in  a  radial  direction.  Their  rear 
edges  are  also  cut  off  longitudinally  so 
that  when  placed  side  by  side  and  forming 
a  lining  for  the  cylinder  A  they  have  con- 
tinuous longitudinal  channels,  E,  parallel 
to  the  elements  of  the  cylinder.  The 
grooves  D  communicate  with  the  channels 
£,  and  thus  allow  the  gas  to  escape  at  the 
top  and  bottom  of  the  mold.  The  interior 
of  the  mold  is  lined  with  refractory  sand. 
Action.  —  When  the  melted  steel  is 
poured  into  the  mold  and  the  ram  R 
forced  down  upon  it,  the  hot  metal  is  at 
first  forced  through  the  openings  O  be- 
tween ram  and  mold.  But  the  metal 
quickly  cools  and  forms  a  solid  mass, 
completely  closing  these  openings  O.  The 
gas  is  forced  out  through  the  channels  as  shown,  and 
the  effect  of  the  pressure  and  shrinkage  is  to  shorten  the 
ingot  about  ij  inches  for  each  foot  of  length. 

Theory. — It  appears  at  first  that  the  metal,  as  well  as  the 
gases,  would  be  expelled  through  the  channels,  and  also 
that,  since  fluid  pressure  is  equal  in  all  directions,  there  is  no 
reason  why  this  pressure  should  force  the  gas  out  of  the 
melted  metal.  Dr.  Siemens  suggests  as  an  explanation  that 
the  steel  cools  first  on  the  exterior  where  it  is  in  contact 
with  the  mold,  and  offers  a  greater  resistance  here  to  the 
motion  of  the  ram.  It  is  broken  up  in  consequence  by  the 
pressure,  and  becomes  porous.  The  interior  of  the  mold 
remaining  fluid,  and  offering  less  resistance  than  the  outside, 
receives  consequently  more  compression,  and  hence  the  re- 
sult will  be  to  force  the  gas  outward  through  the  porous 
exterior.  This  porous  exterior,  while  allowing  the  gas  to 
escape,  retains  the  fluid  metal.  It  is  also  claimed  that  the 
pressure  increases  the  solvent  action  of  the  metal  upon  the 
gases.  Krupp  maintains,  however,  that  this  process  of 


FIG 


GUNS. 


I49 


fluid  compression  simply  closes  up  the  cavities  but  does  not 
-expel  the  gas. 

78.  Treatment  after  Casting  —  Testing  —  Reheating  —  Forging— 
Cranes— Hammer. 

TESTING. — After  the  ingot  is  cast  and  cooled,  specimens 
of  it  are  tested  chemically  to  determine  its  composition, 
and  also  in  the  testing-machine  to  determine  its  physical 
qualities.  The  ingot  is  graded  according  to  these  tests, 
and  a  hole  is  then  bored  through  it  parallel  to  its  axis,  re- 
moving the  central  part  of  the  ingot.  This  hole  is  for 
purposes  of  forging,  as  will  be  explained. 

If  the  ingot  is  short,  this  hole  may  be  punched ;  and  for 
small  tubes  or  any  solid  forgings  the  hole  is  not  necessary. 

REHEATING. — For  forging,  the  ingot  is  then  reheated  in 
a  furnace  which  is  a  modification  of  the  Siemens.  In  the 
reheating,  care  must  be  taken  to  apply  the  heat  slowly  and 
regularly,  so  as  to  avoid  overheating  the  exterior  before 
the  interior  is  brought  to  the  proper  temperature.  If  the 
heat  is  applied  too  quickly,  the  ingot  is  liable  to  crack  from 
unequal  expansion,  and  the  exterior  to  be  overheated  or 
•"  burned." 

CRANES. — The  ingots  when  heated  to  the  proper  temper- 


FIG.  35- 

ature  are  handled  by  heavy  cranes,  which  remove  them  from 
the  furnace  and  carry  them  to  the  hammer  or  press.     They 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

are  slung  from  the  crane  by  a  chain  called  the  sling-chain,, 
and  are  balanced  by  the  addition  of  extra  weights  at  the 
cool  end,  so  that  they  may  be  readily  swung  by  the  work- 
men, and  turned  axially  under  the  hammer.  Fig.  35  shows 
the  general  arrangement  for  forging  an  ingot  under  a  ham- 
mer. H  is  the  hammer,  A  the  anvil,  C  the  crane,  E  the  in- 
got, 5  the  sling-chain,  P  the  porter-bar  ;  the  handles  K  are 
used  for  rotating  the  ingot  under  the  hammer. 

HAMMER. — The  steam-hammer  is  used  in  forging  ingots, 
except  where  hydraulic  pressure  is  preferred.  These  ham- 
mers consist  of  a  heavy  head  or  tup  attached  to  the  piston 
of  a  steam-cylinder.  The  cylinder  is  vertical  and  is  sup- 
ported by  two  legs,  and  the  hammer  thus  formed  is  called 
an  A  hammer,  from  its  general  appearance.  When  the 
steam  raises  the  hammer,  and  is  then  exhausted,  and  the  tup 
allowed  to  fall  by  its  own  weight,  we  have  a  single-acting 
hammer ;  when  the  steam  acts  also  to  drive  the  tup  down, 
we  have  a  double-acting  hammer.  The  foundation  for  the 
anvil  is  separate  from  the  hammer  to  diminish  the  effect  of 
the  blow  upon  the  latter. 

Since  the  same  energy  may  be  obtained  from  a  light 
hammer  moving  quickly  or  from  a  heavy  hammer  moving 
slowly,  the  latter  is  preferred  for  heavy  masses,  as  the  effect 
of  the  blow  is  better  distributed  through  the  mass.  Armor- 
plates  are  generally  made  by  hammering,  as  the  effect  of 
the  blow  is  felt  more  on  the  face  and  less  in  the  interior,  and 
it  is  important  to  have  a  good  quality  of  face.  With  gun- 
forgings  both  hammer  and  hydraulic  pressure  are  used 
with  excellent  results,  the  hydraulic  press,  however,  being 
preferred,  as  it  is  more  slow  in  its  action  and  distributes, 
the  effect  throughout  the  mass. 

79.  Whitworth's  Hydraulic  Forging— The  Press — Mandrels. 

In  this  process  the  ingot  is  drawn  into  shape  by  the 
pressure  of  a  powerful  hydraulic  ram.  As  the  action  is  slow, 
it  is  claimed  that  the  effect  is  better  distributed  throughout 
the  mass,  as  before  stated,  and  consequently  produces  a 
better  effect  upon  the  metal  as  a  whole. 

THE  PRESS. — This  is  a  large  hydraulic  ram  so  arranged 


GUNS.  1^l 

that  it  may  be  quickly  adjusted  to  any  size  of  ingot.  The 
general  arrangement  is  represented  in  Figs.  36  and  37 
although  the  ram  actually  has  many  arrangements  for  ad- 
justment, etc.,  not  shown. 

THE  MANDRELS.— With  this  press  a  secondary  or  mov- 
able anvil,  called  a  mandrel,  is  used.  It  is  shown  in  Figs.  36 
and  37,  and  its  use  is  as  follows  : 

If  the  ingot  is  to  be  drawn  out  into  a  long  forging  such 
as  a  gun-tube,  it  is  first  bored  out  on  the  interior.  It  is 
then  heated,  and  the  mandrel  passed  through  the  bore.  The 
ingot  is  now  placed  under  the  forg ing-press,  resting  on  the 
fixed  anvil  as  shown  in  Fig.  36.  When  pressure  is  applied 


I 


'FRONT.  ELEVATION. 


SIDE  ELEVATION. 


FIG.  36. 


under  these  circumstances,  the  effect  will  be  to  lengthen  the 
ingot,  keeping  its  interior  diameter  unchanged.  On  the 
other  hand,  if  the  ingot  is  to  be  forged  into  a  hoop,  it  is 
bored  as  before,  heated,  and  the  mandrel  passed  through 
the  bore ;  but  in  this  case  the  ends  of  the  mandrel  are  sup- 
ported as  shown  in  Fig.  37,  the  ingot  being  allowed  to  swing 
on  the  mandrel. 

When  the  pressure  is  applied  under  these  conditions,  it 
is  evident  that  the  walls  of  the  ingot  will  be  compressed, 
the  interior  diameter  increased,  and  the  length  of  the  ingot 
will  remain  practically  unchanged. 

In  the  first  case  we  have  a  fixed  mandrel,  and  in  the 
second  a  swinging  mandrel.  A  current  of  water  sometimes 


152 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


circulates  through  the  centre  of  the  mandrels  to  keep  them 
cool,  and  in  the  case  of  the  fixed  mandrel,  it  is  withdrawn 
from  the  forging  by  a  second  hydraulic  press  acting  on  it. 

Comparing  the  hammer  and  press,  it  is  claimed  for  the 
hammer  that  its  effects  are  more  local,  and  therefore  that  it 


FRONT   ELEVATION- 


SIDE  ELEVATION. 


FIG.  37. 


is  better  for  armor-plates ;  that  the  effect  of  its  blows  is  to 
heat  the  metal,  and  therefore  the  temperature  may  be  lower 
in  forging  ;  and  that  it  uncovers  defects  in  the  metal,  while 
the  press  conceals  them. 

80.  Gun-forgings— Treatment   after   Forging — Annealing— Boring 
and  Turning — Oil-tempering — Re-annealing — Tests. 

GUN  FORCINGS. — The  principal  gun-forgings  are  the 
tube,  the  jacket,  and  the  hoops. 

The  forging  of  the  tube  and  hoops  has  been  explained, 
and  that  of  the  jacket  is  exactly  similar. 

ANNEALING. — After  forging,  the  hammer  or  press  leaves 
certain  strains  in  the  metal,  and  they  must  be  removed. 
This  is  done  by  annealing.  This  process  consists  in  heating 
the  forging  carefully  to  a  certain  temperature,  which  is  de- 
termined by  experience,  and  allowing  it  to  cool  slowly,  in 
the  furnace,  the  latter  being  allowed  to  cool  naturally. 
By  this  process  the  steel  becomes  soft,  and  all  strains  are 
removed. 

BORING  AND  TURNING. — The  forging  is  now  placed  in  a 


GUNS.  153 

lathe  and  bored  and  turned  to  near  its  finished  size.  Pieces 
are  also  taken  off  the  ends  as  specimens,  and  tested,  to  de- 
termine the  qualities  of  the  metal  and  as  a  guide  to  subse- 
quent treatment. 

OIL-TEMPERING. — The  object  of  this  process,  to  which 
the  forging  is  now  subjected,  is  to  give  the  peculiar  prop- 
erty called  "  toughness"  to  steel.  The  practical  effect  is 
that  it  increases  the  elastic  limit  and  tensile  strength,  and 
reduces  the  elongation  before  rupture. 

Process. — The  forging  is  slowly  heated  and  carefully 
inspected,  till  all  the  parts  have  acquired  the  same  tem- 
perature, which  is  judged  by  the  color.  A  long  forging  is 
generally  heated  vertically  to  avoid  warping.  When  at 
the  proper  temperature,  it  is  raised  by  a  crane  and  lowered 
vertically  into  a  tank  of  oil,  a  current  of  which  is  caused  to 
flow  through  the  bore.  The  oil  is  surrounded  by  a  water- 
jacket  to  keep  down  the  temperature. 

Being  a  poor  conductor  of  heat,  the  oil  allows  the  steel 
to  cool  correspondingly  slowly,  and  thus  gives  the  particles 
time  to  adjust  themselves,  and  the  result  is  a  considerable 
increase  in  elasticity  and  tenacity,  and  it  acquires  the  prop- 
erty of  toughness  already  defined. 

RE-ANNEALING. — The  process  of  oil-tempering  causes 
internal  strains  in  the  metal,  and  these  are  removed  by 
reannealing  as  before.  This  annealing  process  reduces 
slightly  the  elastic  limit  and  tensile  strength  and  increases 
the  elongation  before  rupture. 

TESTS.— The  physical  qualities  of  the  metal  are  now 
tested.  For  this  purpose  specimens  are  cut  from  the 
breech  and  muzzle  ends  of  each  tube,  jacket,  or  hoop  forg- 
ing, and  the  results  of  these  tests  compared.  No  great 
difference  in  quality  must  exist  between  breech  and  muzzle 
specimens,  as  this  would  indicate  a  variation  in  quality  of 
the  metal  from  breech  to  muzzle.  In  the  U.  S.  service  the 
requirements  of  the  Ordnance  Department  are  about  as 
follows  : 

Elastic  limit,  46,000  to  50,000  pounds  per  square  inch ; 

Tensile  strength,  86,000  to  93,000  pounds  per  square 
inch ; 


154  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Elongation  at  rupture,  15  to  17  per  cent  in  a  length  of  3 
inches. 

81.  Brinell's  Experiments. 

To  determine  the  effects  of  heating  and  cooling  on  the 
change  of  structure  and  the  hardening  of  steel,  Mr.  J.  A. 
Brinell,  a  Swedish  engineer,  made  a  series  of  experiments. 

Taking  a  certain  kind  of  steel  which  contained  about  the 
same  percentage  of  carbon  as  gun-steel,  he  heated  bars  of 
it  to  different  temperatures  and  cooled  them  at  different 
rates.  After  heating  and  cooling,  the  bars  were  broken 
and  the  fracture  carefully  examined,  and  chemical  tests 
were  made  to  determine  the  condition  of  the  carbon.  He 
found  that  there  were  two  states  of  the  carbon — one  which 
he  called  free  carbon  and  which  was  associated  with  soft 
steel,  and  the  other,  fixed  carbon,  associated  with  hard 
steel.  In  general  the  soft  steel  had  a  crystalline  structure 
and  the  hard  steel  an  amorphous  structure,  or  one  in 
which  the  crystals  were  so  small  as  to  lose  their  crystalline 
appearance. 

His  conclusions  were  as  follows  : 

1.  For  each  steel,  hard  and  soft,  there  is  a  certain  tem- 
perature, called  the  critical  temperature,  to  which  if  the 
steel  be  heated,  and  be  suddenly  cooled,  all  the  carbon  will 
become  fixed,  and  the  structure  will  be  amorphous.     This 
is  the  hardest  condition  of  steel ;  and  hence,  to  harden  it,  it 
is  heated  to  this  temperature  and  cooled  suddenly. 

2.  Hard  steel,  if  heated  to  this  critical  temperature  and 
cooled  slowly,  will  acquire  the  crystalline  structure,  and  all 
the  carbon  will  become  free.     Soft  steel  heated  to  this  tem- 
perature and  cooled  slowly  undergoes  no  change.     This  is 
the  softest  condition  of  steel,  and  hence,  to  anneal  it,  it  is 
heated  to  this  critical  temperature  and  cooled  slowly. 

3.  If  hardened  steel,  or  steel  which  has  been  subjected 
to  the  first  process,  be  heated  to  any  temperature  below 
the  critical  temperature,  it  becomes  softer  as  the  tempera- 
ture increases.     That  is,  with  hard  steel,  as  the  critical  tem- 
perature is  approached,  more  and  more  of  the  fixed  carbon 
becomes  free,  and  if  the  steel  be  cooled  either  slowly  or 


GUNS.  155 

quickly  after  having  been  heated  to  any  temperature  below 
the  critical  one,  the  hardness  of  the  steel  is  diminished. 
This  process  is  called  tempering,  and  by  it  the  degree  of 
hardness  can  be  regulated  to  any  extent.  It  is  the  process 
commonly  employed  by  the  blacksmith  in  tool-making. 
The  less  the  steel  is  heated  the  harder  it  will  be. 

4.  When  steel  is  heated  to  the  critical  temperature  and 
cooled  very  quickly,  as  by  immersion  in  mercury  or  acidu- 
lated water,  it  becomes  harder  than  if  cooled  by  immersion 
in  ordinary  water ;  and  on  the  other  hand,  if  cooled  more 
slowly,  as  in  oil,  it  acquires  less  hardness  but  more  elas- 
ticity. 


MACHINES   USED   IN   GUN-MANUFACTURE. 

82.  General  Principles  of  Machines — Definition — How  Motion  is 
Transmitted  and  Modified. 

In  order  to  understand  the  operations  in  the  manufac- 
ture of  a  modern  gun,  some  knowledge  of  the  general 
principles  of  machines  is  necessary,  since  all  the  operations 
upon  the  gun  after  the  forgings  are  received,  are  conducted 
in  a  machine-shop,  and  the  success  of  the  modern  gun  as  a 
machine  for  propelling  projectiles,  depends  upon  the  accu- 
racy with  which  the  machine-work  is  done  in  building  it. 

DEFINITION. — A  machine  is  any  instrument  or  device 
designed  to  receive  energy  from  some  source,  and  to  over- 
come certain  resistances  in  transferring  this  ene'rgy  to  other 
bodies.  (Michie,  p.  246.) 

The  mechanical  principles  of  machines  are  discussed  in 
the  Mechanics,  pages  246-281,  and  it  is  intended  here  to. 
give  the  practical  application  of  these  principles  as  seen  in 
the  shops. 

Another  definition  of  a  machine  is,  an  assemblage  of 
moving  parts  for  the  purpose  of  transmitting  and  modify- 
ing motion  and  energy. 

How  MOTION  is  TRANSMITTED  AND  MODIFIED. — A 
machine  receives  its  motion  from  some  source  of  energy 
such  as  the  steam-engine,  water-wheel,  etc.,  and  transmits  it. 


156  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

through  a  series  of  wheels,  sliding  surfaces,  etc.,  to  the 
point  where  the  work  is  done. 

The  source  of  motion  is  called  the  driving-point  or  prime 
mover ;  the  parts  through  which  the  motion  is  transmitted, 
the  train  ;  and  the  point  where  the  work  is  done,  the  working- 
point. 
v      Motion  may  be  transmitted  and  modified  by  : 

1.  Rolling  contact  of  two  or  more  surfaces  ; 

2.  Sliding  contact,  as  in  gear-wheels,  screws,  etc. 

3.  Belts  or  bands  ; 

4.  Linkwork  ; 

5.  Cords  or  ropes  ; 

6.  Hydraulic  connection. 

83.  Rolling  Contact — Different  Forms  of  Pieces  in  Rolling  Contact. 
ROLLING  CONTACT. — Let  A  and  B,  Fig.  38,  represent  two 
wheels  whose  axes  are   parallel.     When 
motion  is  communicated  to  B  it  will  impart 
this  motion  to  A  by  the  friction  of  the  two 
surfaces  in  contact  at  the  point  a.     These 
FIG.  ?8.  circles  in  contact  at  a  are  called  the  pitch- 

circles,  or  pitch-lines  ;  the  point  of  contact  a,  the  pitch-point. 
The  line  cd  joining  the  centres  of  the  wheels  is  called  the 
line  of  connection,  and  is  the  line  along  which  the  velocity  of 
the  moving  pieces  is  zero. 

The  general  principle  which  governs  the  motion  of  the 
pieces  in  rolling  contact  is  that  each  pair  of  points  in  the 
pitch-lines  which  are  in  contact  at  any  instant,  must  at  that 
instant  be  moving  in  the  same  direction,  and  with  the  same 
velocity. 

This  principle  leads  to  the  following  results  : 
Since  each  pair  of  points  in  contact  must  move  in  the 
same  direction  at  the  same  instant,  the  axes  of  the  wheels 
and  their  points  of  contact  must  lie  in  the  same  plane,  be- 
cause the  motion  of  the  points  of  contact  is  at  right  angles 
to  the  axis  of  each  wheel  ;  and  since  the  velocities  of  their 
points  of  contact  must  be  equal,  the  angular  velocities  of 
the  wheels  must  be  inversely  as  their  radii. 


GUNS.  157 

DIFFERENT  FORMS  OF  PIECES  IN  ROLLING  CONTACT.— 
Besides  the  circular  wheels,  we  may  have — 

1.  A  wheel,  A,  and  rack,  £,  Fig.  39, 

2.  Two  wheels  with  intersecting  axes,  Fig.  40  ; 

3.  Two  wheels  with  axes  which  are  neither  parallel  nor 
intersecting.     This  case  will  not  be  considered. 


FIG.  39. 

For  the  wheel  and  rack,  since  all  points  in  the  wheel  move 
at  right  angles  to  its  axis,  while  all  points  of  the  rack  move 
parallel  to  itself,  or  at  right  angles  to  the  axis  of  the  wheel, 
the  general  principle  that  the  points  of  contact  shall  be  moving 
in  the  same  direction  requires  that  the  axis  of  the  wheel  and 
all  points  of  contact  must  lie  in  a  plane  perpendicular  to  the 
motion  of  the  rack,  and  that,  since  the  points  of  contact  must 
have  the  same  velocity,  the  actual  velocity  of  the  rack  must  be 
equal  to  the  product  of  the  angular  velocity  of  the  wheel  by 
its  radius.  For  the  two  wheels  with  intersecting  axes,  if  the 
line  ac  joining  the  point  of  contact  a  with  the  intersection  of 
the  axes  be  regarded  as  the  line  of  contact  of  two  cones, 
whose  axes  are  those  of  the  wheels,  it  is  evident  that,  as  the 
surfaces  of  the  cones  come  into  contact  along  this  line,  each 
pair  of  points  in  contact  will  be  moving  at  that  instant  in 
the  same  direction  and  with  the  same  velocity.  Hence  the 
surfaces  of  two  wheels  whose  axes  intersect,  are  frusta  of 
cones,  whose  element  of  contact  passes  through  the  point  of 
intersection  of  the  axes. 

84.    Sliding    Contact— Principles  of   Teeth— Figures  of   Teeth- 
Action. 

SLIDING  CONTACT. — In  the  method  of  communicating 
motion  by  rolling  contact,  it  is  evident  that  no  great  force 


IS  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

can  be  transmitted  without  danger  of  the  slipping  of  one 
wheel  on  the  other.  If  this  happens,  the  velocity  ratio  of 
the  two  wheels  is  not  constant,  and  hence  this  method  will 
not  answer  for  accurate  work.  Where  an  exact  ratio  is  to 
be  maintained  between  the  velocities  transmitted  by  two 
wheels,  these  wheels  must  be  so  connected  that  one  cannot 
move  without  the  other. 

This  connection  is  usually  made  by  means  of  projections 
on  each  wheel  called  teeth. 

PRINCIPLES  OF  TEETH. — Their  construction  and  opera- 
tion depend  on  the  following-  general  principles  : 

Let  A  and  B,  Fig.  41,  represent  two  wheels  whose  axes 
are  a  and  b,  and  suppose  these  wheels 
in  contact  at  c. 

Then  the  circumferences  in  con- 
tact are  the  pitch-circles,  as  before 
explained.  Let  i,  2,  3,  etc.,  represent 
teeth  formed  upon  the  wheel  A. 
Then  the  pitch  of  the  teeth  is  the 
distance  de  along  the  pitch-circle 
from  the  front  of  one  tooth  to  the  front  of  the  next.  Hence — 

1.  In  wheels  which  rotate  continuously  for  one  revolu- 
tion or  more,  the  pitch  must  be  some  aliquot  part  of  the 
pitch-circle,  in  order  that  it  may  be  contained  in  that  circle 
an  even  number  of  times.     For  a  rack,  or  a  wheel  which 
does  not  perform  a  complete  revolution,  this  condition  is 
not  necessary. 

2.  In  order  that  two  wheels,  or  a  wheel  and  rack,  may 
work  correctly  together,  the  pitch  must  be  the  same  in  each. 

3.  Hence,  in  a  pair  of  wheels  which  work  together,  the 
number  of  teeth  in  each  wheel  is  directly  as  the  circumfer- 
ence or  radius,  and  therefore  inversely  as  the    number  of 
revolutions  in  a  given-  time. 

FIGURES  OF  TEETH. — These  are  regulated  by  the  prin- 
ciple that  the  velocity  ratio  given  by  the  teeth  sliding  on 
each  other  shall  be  the  same  as  that  given  by  the  pitch- 
circles  rolling  on  each  other. 

ACTION  OF  TEETH.  — To  give  a  general  idea  of  this  ac- 
tion, let  Fig.  42  represent  the  teeth  of  two  wheels  in  contact. 


GUNS. 


'59 


DRIVEN 


DRIVER 

FIG.  42. 


The  tooth  a  of  the  lower  wheel  first  touches  b  of  the 
upper  at  the  point  c.  These  teeth  then  slide  towards  each 
other  till  the  point  d  is  reached, 
when  they  slide  away  from  each 
other  and  finally  lose  contact  at  e. 
This  process  continues  for  all  the 
teeth,  the  arc  cd  being  the  arc  of 
approach,  and  de  the  arc  of  recess, 
the  whole  curve  cde  representing 
the  various  positions  occupied  by  the  point  of  contact  dur- 
ing the  action  of  the  teeth. 

The  method  of  describing  the  figures  of  teeth  is  too  ex- 
tensive for  discussion  here. 

85.  Belts  or  Bands — Rounded  or  Crowning  Pulleys — Speed-Cones — 
Starting  and  Stopping. 

BELTS. — When  teeth  are  used  to  communicate  motion, 
they  possess  the  great  advantage  of  preserving  always  the 
same  velocity  ratio  between  two  wheels.  They  have,  how- 
ever, the  disadvantage  of  being  a  rigid  connection,  so  that 
they  do  not  allow  for  starting  or  stopping,  or  sudden 
changes  of  speed.  Hence  for  the  transmission  of  energy 
from  the  engine  or  other  prime  mover  to  the  different  ma- 
chines in  a  shop,  belts  are  almost  universally  employed. 
After  the  energy  has  been  received  at  any  machine,  the 
parts  of  that  machine  are  connected  by  gearing,  or  teeth,  if 
accurate  velocity  ratios  are  required. 

Belts  are  generally  made  of  leather  or  gutta  percha,  and 
are  broad  and  flat,  and  hence  require  correspondingly  shaped 
pulleys. 

The  velocity  ratio  of  two  pulleys  connected  by  a  belt 
follows  the  same  principle  as  in  the  case  of  rolling  or  sliding 


FIG.  43.  FIG.  44. 

contact,  viz.,  the  actual  velocities  of   all  points  along   the 
belt  are  the  same,  and  hence  the  angular  velocities  of  the 


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TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


\ 

.1— 


pulleys  are  inversely  as  the  radii.  If  the  pulleys  are  to 
move  in  the  same  direction,  the  belt  must  be  open,  Fig.  43  ; 
if  in  opposite  directions,  the  belt  must  be  crossed,  Fig.  44. 

ROUNDED  PULLEY. — To  prevent  the  belt  from  leaving 
the  pulley,  the  latter  is  made  crowning  or  rounded,  Fig.  45. 
j  A  belt  always  moves  toward  that  part 

of  the  pulley  whose  radius  is  greatest,  and 
the  reason  is  as  follows  :  When  the  belt 
3  moves  to  one  side  of  the  pulley,  the  side 
ab  of  the  belt  becomes  compressed,  Fig. 
45.  The  resistance  of  the  side  ab  to  this 
compression  produces  a  force  in  the  direc- 
tion of  the  arrow  e,  which  straightens  the 
belt  and  causes  it  to  move  to  the  highest, 
part  of  the  pulley. 

SPEED-CONES. — To  vary  the  velocity 
ratio  communicated  between  a  pair  of  par- 
allel pulleys  or  shafts  by  a  belt,  without  stopping  the  mo- 
tion of  the  machinery,  speed-cones  are  used.  These  may 
be  either  continuous  cones, 
Fig.  46,  or  stepped  cones,  Fig. 
47.  In  the  first  case  we  can 
obtain  a  gradual  variation  of 
speed,  and  in  the  second,  cer- 
tain fixed  variations  only. 

The  second  method  is  gen- 
erally used. 

STARTING  AND  STOPPING. 


j 

Q- 


FIG.  46. 


FIG.  47. 


— As  individual  machines  require  to  be  started  or  stopped 
without  interfering  with  the  source  of  power,  each  machine 
is  in  general  provided  with  two  pulleys. 

These  pulleys  are  mounted  on  an  independent  shaft  called 
a  counter-shaft,  and  one  of  them  is  fixed  to  this  shaft,  while 
the  other  turns  freely  upon  it.  When  the  machine  is  to  be 
stopped,  the  belt  is  shifted  to  the  "  loose  pulley,"  as  it  is 
called  ;  and  when  started,  to  the  fixed  pulley. 

86.  Linkwork— Cords  and  Ropes— Hydraulic  Connection. 

LlNKWORK. — When  two  rotating  pieces  are  connected 


GUNS.  l6l 

by  a  rigid  bar,  as  the  driving-wheels  of  a  locomotive,  this 
bar  is  called  a  link.  It  may  also  connect  a  rotating  piece 
and  a  sliding  piece,  as  the  piston-rod  and  crank  of  a  steam- 
engine,  which  are  connected  by  a  link.  In  the  case  of  link- 
work,  the  velocity  of  all  points  of  the  link  being  the  same 
at  any  instant,  the  angular  velocities  of  the  rotating  pieces 
are  inversely  as  the  perpendiculars  let  fall  from  the  axes  of 
rotation  to  the  link. 

In  the  case  of  a  rotating  and  a  sliding  piece,  as  in  Fig. 
48,  every  point  of  the  sliding  piece  is  moving  at  a  given  in- 
stant perpendicular  to  the  line  ab, 
and  at  the  same  instant  the  point 
c  is  moving  perpendicular  to  be. 
Hence  a  line  through  the  point  b, 
perpendicular  to  the  plane  of  the 
paper  at  the  intersection  of  these 
two  lines,  is  at  this  instant  the  in- 
stantaneous axis  about  which  the 
two  points  a  and  c  are  moving. 

Their  velocities  are  therefore 
directly  as  their  distances  from  this 
axis,  or 

v :  v'  ::  ab  :  cb.  FIG.  48. 

The  same  principle  may  be  applied  to  linkwork  in  gen- 
eral. The  actual  velocity  of  the  point  a  becomes  zero  when 
the  point  c  reaches  the  positions  i  and  2,  and  these  points 
are  called  "  dead-points."  In  the  steam-engine  the  stored-up 
energy  of  the  fly-wheel  carries  the  point  c  over  the  dead- 
points. 

CONNECTION  BY  CORDS. — This  connection  is  principally 
made  between  blocks,  forming  a  block  and  fall,  or  block  and 
tackle. 

Although  very  useful,  it  is  not  employed  to  any  extent 
in  machine  construction.  Wire  ropes  are  sometimes  used 
instead  of  belts  to  transmit  power,  in  which  case  grooved 
pulleys  are  required  to  keep  the  rope  from  slipping  off. 

HYDRAULIC  CONNECTION. — This  is  of  great  importance 
in  modern  machinery,  as  the  gun-steel  is  forged  by  a  hydrau- 


102  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

lie  press,  and  hydraulic  cranes  are  employed  for  lifting-  the 
heavy  weights.  The  general  principle  of  these  machines  is 
explained  in  mechanics,  and  depends  on  the  fact  that  if  two 
cylinders  fitted  with  pistons  are  in  hydraulic  communication, 
the  volume  of  liquid  forced  out  of  one  is  equal  to  that  forced 
into  the  other.  As  this  volume  is  the  product  of  the  length 
of  the  cylinder  by  its  area  of  cross-section,  it  follows  that 
the  velocities  of  the  pistons  are  inversely  as  their  areas. 
From  this  principle  we  can  obtain  a  slow  motion  and  great 
power,  as  in  the  hydraulic  press,  or  a  quick  motion  and  less 
power,  as  in  the  hydraulic  crane,  by  regulating  properly 
the  size  of  the  cylinder. 

87.    General    Arrangement     of    Machine-shops  —  Distribution    of 

Energy. 

GENERAL  ARRANGEMENT. — All  machine-shops  are  ar- 
ranged upon  the  same  general  principles,  though  differing 
greatly  in  details,  depending  on  the  work  to  be  done. 

In  general,  there  is  first  a  source  of  energ}%  as  a  steam- 
engine  or  water-wheel.  This  source  of  energy  may  be 
regarded  as  the  reservoir  from  which  energy  is  drawn  as 
required  ;  and  as  different  amounts  of  energy  are  needed  at 
different  times,  according  as  different  machines  are  working 
or  not,  some  arrangement  must  be  made  to  regulate  the 
amount  of  energy.  Without  this  regulation,  if  several 
machines  are  suddenly  stopped,  the  energy  will  be  in  excess, 
and  the  remaining  machines  will  increase  in  speed.  This  is 
injurious  to  the  work  and  to  the  machines.  The  reverse 
will  happen  when  machines  are  suddenly  started.  To  regu- 
late the  energy  of  the  prime  mover,  a  fly-wheel  and  governor 
are  used.  The  fly-wheel  stores  up  energy  and  gives  it  out 
when  it  is  suddenly  required,  and  prevents  sudden  changes 
in  speed,  and  the  governor  regulates  the  supply  of  steam, 
etc.,  to  the  engine. 

The  principles  are  explained  in  mechanics. 

DISTRIBUTION  OF  ENERGY. — To  distribute  the  energy 
from  the  prime  mover  to  the  various  machines,  any  one  of 
the  methods  previously  described  may  be  used.  Belts  are 
generally  preferred. 

The  pulleys  which  carry  these  belts  run  upon  lines  of 


GUNS. 


163 


-shafting.     Extending  lengthwise  through  the  shop,  there  is 
a  "  main  shaft,"  a,  Fig.  49. 

The  motion  is  communicated  directly  from  the  prime 
mover  b  to  this  main  shaft,  by  a  belt.  The  shaft  is  supported 
by  hangers,  c,  bolted  to  the  beams  or  walls.  At  intervals 
along  the  main  shaft  are  pulleys,  d,  each  of  which  carries 
the  belt  for  a  particular  machine. 


d 


d 


FIG.  49. 

Over  each  machine  is  a  short  shaft,  e,  called  a  counter- 
shaft. 

This  carries  at  least  three  pulleys,  the  first  running  loose 
upon  the  shaft,  the  second  fixed  to  it,  and  the  third  also  fixed, 
and  driving  the  machine.  Their  use  has  been  explained. 

In  addition  to  affording  a  means  of  starting  and  stopping 
any  machine  without  interfering  with  the  main  shaft,  the 
counter-shaft  affords  a  means  of  increasing  or  decreasing  the 
speed  of  any  machine,  by  decreasing  or  increasing  the  size 
of  the  pulleys  as  compared  with  those  on  the  main  shaft 
which  transmit  the  power. 

88.  Machine-tools— Shearing— Cutting— Scraping— Drills— Reamers 

and  Milling-cutters. 

In  every  machine  the  working  point,  or  part  by  which 
the  work  is  actually  done,  is  called  a  tool.  Machine-tools 


164 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


may  be  classified  according  to  the  manner  in  which  they 
act,  as— 

1.  Shearing- tools ; 

2.  Cutting  or  paring-tools  ; 

3.  Scraping-tools. 

SHEARING-TOOLS. — These  tools  act  to  divide  a  plate  or 
bar  of  the  material  operated  on,  by  causing  the  parts  to 
separate  from  each  other  by  sliding  or  shearing.  This  class 
includes  also  punches  and  dies.  They  are  not  used  to  any 
extent  in  gun-construction. 

CUTTING-TOOLS. — These  cut  a  thin  chip  or  shaving  from 
the  surface  of  the  work  and  thus  produce  a  new  surface. 

SCRAPING-TOOLS. — These  tools  scrape  off  small  particles 
from  the  surface  of  the  work,  and  correct  any  irregularities 
that  may  have  been  left  by  the  cutting-tool. 

ACTION  OF  CUTTING  AND  OF  SCRAPING-TOOLS. — The 
general  method  of  the  action  of  these  tools  is  shown  in 
Figs.  50  and  51. 


E 


In  each  case  the  tool  is  acting  upon  a  cylindrical  piece 
of  work  which  is  rotating  in  the  direction  of  the  arrow. 

The  angle  DAE  is  called  the  cutting  angle  of  the  tool  ; 
DAC,  the  angle  of  relief,  the  line  AC  being  tangent  to  the 
face  of  the  work  at  the  point  A.  The  angle  CAE  is  the 
working  angle,  and  is  equal  to  DAC '  +  DAE. 

In  cutting-tools  the  angle  CAE  is  always  acute  ;  in 
scraping-tools  the  angle  CAE  is  either  right  or  obtuse  :  and 
the  tools  are  thus  distinguished  by  their  working  angles. 

The  hook  F  is  given  to  the  tools  in  order  that  the  cutting 
edge  A  shall  not  be  above  the  axis  or  centre  line  of  the  tool. 

If  this  were  the  case,  any  springing  of  the  cutting  edge 


G  UNS. 


I65 


caused  by  excessive  resistance  of  the  material,  would  move 
the  edge  A  further  into  the  work,  or  cause  it  to  "  dig  into  " 
it,  while  as  arranged  the  cutting  edge  will  spring  away 
from  the  work.  In  plan,  the  tool  may  be  of  various  shapes, 
as  shown  in  Fig.  52,  these  shapes  depending  on  the  nature 
of  the  work. 


c 


FIG.  52. 

DRILLS  AND  REAMERS. — For  making  cylindrical  holes, 
drills  and  reamers  are  used.  The  ordinary  drill  is  shown  in 
Fig.  53,  the  cutting  edge  being  adb\ 
the  reamer  in  Fig.  54. 

The  reamer  consists  of  a  num- 
ber of  parallel  cutters  forming  a 
cylinder,  and  is  used  to  finish  a 
cylindrical  hole  that  is  required  to 
be  very  true  and  smooth.  Drills 
and  reamers  rotate  about  the  ver- 
tical axis  cd  and  have  generally  a 
motion  in  the  direction  of  this  axis. 

MILLING-CUTTERS. — These  may 
be  used  to  form  surfaces  of  almost 
any  shape,  and  they  vary  greatly  in 
form.  The  general  method  of  their 
operation  is  indicated  in  Fig.  55,  in 
which  the  irregular  surface  abed  is  cut  by  the  milling-cutter 
A  rotating  on  the  axis  B. 


^ 

d 

FIG.  53. 


FIG.  54. 


FIG.  55. 

The  work  C  moves  along  a  plane  director  at  right  angles 
to  the  axis  B. 


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TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


89.  Machines  in  General  Use — The  Lathe — Parts. 

MACHINES  IN  GENERAL  USE. — The  machines  in  general 
use  are 

The  lathe  ; 
The  planer ; 
The  shaper ; 
The  drill-press; 
The  milling-machine. 

THE  LATHE. — This  machine  is  intended  principally  to 
produce  accurate  surfaces  of  revolution.  Its  general  ar- 
rangement is  as  follows: 

A  piece  of  metal  or  wood  is  caused  to  revolve  about  one 
of  its  lines  as  an  axis.  A  cutting-  or  scraping-tool  is  made  to 
bear  against  the  metal  or  wood.  As  the  latter,  which  is 
called  the  "  work,"  revolves,  the  tool  is  caused  to  move 
either  parallel  or  perpendicular  to  the  axis  of  the  work,  or 


FIG.  56. 


in  a  direction  which  is  compounded  of  these  two  motions. 
The  tool  cuts  a  chip  or  shaving  from  the  surface  of  the 
work,  and  by  a  continuation  of  its  action  produces  either  a 
cylinder,  a  plane  surface,  a  cone,  or  any  other  surface  of 


GUNS. 


I67 


revolution  which  may  be  formed  by  combining  the  two 
motions  at  right  angles  to  each  other. 

PARTS. — The  principal  parts  of  the  lathe,  Fig.  56,  are  the 
bed,  consisting  of  two  parallel  ways  or  guides,  a,  of  a  A- 
shaped  cross-section. 

On  these  guides  slides  the  support  for  the  tool,  which  is 
thus  made  to  travel  parallel  to  the  axis  of  the  work.  At  one 
end  of  the  ways  is  fixed  a  heavy  block  of  metal,  b,  called  the 
head-stock.  This  forms  a  support  for  the  spindle  c.  To  this 
spindle  (see  Fig.  57)  is  attached  the  face-plate  d,  by  means 
of  a  screw,  d ',  on  the  end  of  the  spindle.  This  spindle  is 
hollow  at  one  end,  and  in  this  hollow  fits  a  conical  piece  of 
metal,  e,  called  the  live-centre.  The  spindle  also  carries  a 
speed-cone,/,  and  a  gear-wheel,  g.  The  gear-wheel  is  fixed 
to  the  spindle,  while  the  cone  revolves  freely  upon  it.  The 
gear-wheel^  and  cone /may  be  connected  by  a  bolt,  i,  pass- 
ing through  g.  The  small  end  of  the  speed-cone  terminates 
in  a  gear-wheel,  //,  which  is  a  part  of  the  cone,  and  hence 
runs  free  on  the  spindle,  but  revolves  with  the  same  angular 
velocity  as  the  cone.  Parallel  to  the  lathe-spindle  c  is  an- 
other axis,  k,  Fig.  57,  carrying  two  toothed  wheels,  k'  and/£". 


k 


U 


FIG.  57- 


This  axis  k  is  mounted  in  eccentric  bearings,  and  may  be 
moved  so  that  its  wheels,  k'k" ,  will  engage  or  disengage  with 
those  on  the  lathe-spindle  c.  The  arrangement  of  the  axis 
k  and  wheels  k'  and  k"  is  called  the  back  gear.  At  the  op- 
posite end  of  the  lathe-bed  is  a  second  block  of  metal,  b'r 
resting  on  the  ways,  called  the  tail-stock.  It  also  supports 
a  spindle,  called  the  dead-spindle,  and  this  spindle  termi- 


1 68  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

nates  in  a  conical  piece  of  metal,  er,  called  the  dead-centre  or 
back  centre.  The  tail-stock  may  be  moved  to  any  position 
along  the  ways,  and  clamped  there,  and  the  dead-spindle 
has  a  sliding  motion  parallel  to  the  axis  of  the  lathe,  which 
enables  the  distances  between  the  centres  e  and  e'  to  be  very 
accurately  adjusted.  These  centres  e  and,  /,  form  the  axis 
of  revolution  for  any  work  in  the  lathe ;  and  if  they  are  re- 
moved, the  prolongation  of  the  axis  of  the  live  and  dead 
spindles  forms  this  axis. 

BO.  The  Lathe— Slide-rest— Feed— Action. 

SLIDE-REST. — This  forms  the  support  for  the  cutting- 
tool,  and  through  it  motion  is  given  to  the  tool  in  any  direc- 
,  0     t  tion.     It  consists  (Fig.  58)  of  a 

slide  or  bed,  /,  resting  upon  the 
ways,  a,  of  the  lathe,  and  ca- 
pable of  travelling  along  them 
by  the  action  of  the  feed- 
screw m.  Upon  this  slide 
rests  a  second  or  cross  slide,  n, 
which  moves  at  right  angles 
to  the  first  slide,  and  hence  at  right  angles  to  the  axis  of 
the  lathe.  This  cross-slide  carries  a  tool-holder,  o. 

FEED. — The  screw  m  is  called  the  feed-screw.  It  passes 
through  a  nut,  m' ',  on  the  slide-rest,  and  this  nut  is  made  in 
halves  which  can  be  separated,  thus  freeing  the  nut  from 
the  feed-screw,  and  stopping  the  longitudinal  travel  of  the 
slide-rest.  The  cross-feed  is  given  by  hand  or  automati- 
cally by  gearing,  by  means  of  the  screw  ri.  On  one  end  of 
the  feed-screw  m  is  fixed  the  gear-wheel  /  (Fig.  56).  At- 
tached to  the  lathe-spindle  is  a  second  gear-wheel,  /»',  and 
upon  an  axis  fixed  to  the  head-stock  or  some  convenient 
part  of  the  lathe-bed  is  a  third  gear-wheel,  p" .  This  ar- 
rangement may  be  varied  according  to  circumstances,  and 
is  intended  to  regulate  the  velocity  ratio  of  the  lathe-spindle 
and  that  of  the  feed-screw.  .Suppose,  for  example,  it  is  re- 
quired to  cut  a  screw  having  ten  threads  to  the  inch,  and 
that  the  feed-screw  of  the  lathe  has  this  number.  Then  it 
is  evident  that  the  work  must  turn  ten  times  while  the  tool 


GUJVS.  169 

moves  one  inch,  and  also  that,  in  order  to  move  the  tool  one 
inch,  the  feed-screw  must  turn  ten  times.  In  other  words, 
the  velocity  ratio  of  the  feed  screw  and  of  the  work  is 
that  of  equality.  Hence,  from  what  has  been  stated  under 
Toothed  Wheels,  it  follows  that  p  and  p'  must  have  the 
same  number  of  teeth.  The  number  of  teeth  upon  p"  will 
not  affect  the  velocity  ratio,  since,  being  a  lever  of  equal 
arms,  it  receives  and  transmits  the  motion  from  /  to/'  with- 
out change. 

ACTION  OF  LATHE. — Motion  is  imparted  to  the  lathe 
from  the  belt  running  on  the  speed-cone  /.  By  placing  the 
belt  on  the  different  steps  of  this  cone  considerable  varia- 
tion of  speed  may  be  obtained.  If  a  slower  speed  than  that 
given  by  the  cone  is  desired,  the  back  gear  is  used.  The 
action  of  the  back  gear  is  as  follows  : 

When  the  back  gear  is  in  gear  with  the  lathe,  the  cone- 
pulley  is  detached  from  the  large  gear  g  by  removing  the 
bolt,  z,  Fig.  57.  The  cone-pulley  then  rotates,  and  its  small 
gear  h  drives  the  large  wheel  k'  of  the  back  gear.  The 
speed  of  the  back-gear  shaft  is  thus*  reduced  in  the  inverse 
ratio  of  the  numbers  of  teeth  of  h  and  k' ,  and  with  this 
reduced  speed  the  gear  k"  drives  g,  which  in  turn  drives 
the  lathe-spindle.  The  speed  is  again  reduced  here  in  the 
inverse  ratio  of  the  numbers  of  the  teeth  of  g  and  k". 

The  action  of  the  feed-screw  is  evident.  By  throwing 
the  feed-screw  out  of  action  and  causing  the  cutting-tool  to 
move  at  right  angles  to  the  axis  of  the  lathe  by  the  screw 
ri  a  plane  surface  will  be  formed,  and  by  combining  the 
longitudinal  and  transverse  motions  in  various  ways  any 
surface  of  revolution  may  be  produced. 

91.  The  Planer— Parts— Action. 

The  object  of  this  machine  is  to  make  a  flat  surface, 
as  nearly  plane  as  possible.  Its  general  principles  are  as 
follows  : 

A  large  table  is  made  to  slide  along  two  parallel  plane 
surfaces.  Upon  this  table  is  fixed  the  work.  Above  the 
table  the  cutting-tool  is  firmly  supported.  As  the  table 
slides,  the  tool  bears  against  the  work,  and  cuts  a  chip  or 


TEXT-BOOK   Of    ORDNANCE  AND    GUNNERY. 


shaving,  leaving  a  surface  which  is  an  exact  copy  of  the 
parallel  plane  guiding  surfaces  of  the  table.  The  table  and 
work  then  slide  back,  and  at  the  end  of  this  motion  the  cut- 
ting-tool is  moved  sidewise  an  amount  equal  to  the  width 
of  the  cut.  This  side  motion  is  called  the  feed.  The  table 
with  the  work  again  moves  forward,  and  the  tool  makes  a 
second  cut,  and  these  operations  are  repeated  till  the  work 
is  finished. 

PARTS. — The  machine  (Fig.  59)  consists  of  a  bed,  a,  which 
is  essentially  two  parallel  beams  or  cheeks  having  on  the 


FIG.  59- 

upper  surfaces  two  V-shaped  grooves,  which  are  the  guide- 
grooves.  The  table  b  has  two  corresponding  projections 
on  its  under  side  which  fit  into  these  guide-grooves.  Along 
the  middle  of  the  under  side  of  the  table  is  a  rack,  c,  into 
which  gears  a  toothed  wheel,//, by  which  the  table  is  driven. 
Two  vertical  standards,  e,  support  a  cross-slide,  f,  and  this 
cross-slide  carries  the  tool-holder  /'  and  tool.  The  cross- 
slide  can  be  raised  or  lowered  upon  the  standards  by  the 
screws  g,  acted  on  by  the  bevel  gears  h.  A  feed-screw,  k, 


GUNS.  171 

runs  through  the  cross-slide,  and  gives  the  feed  motion 
already  spoken  of  to  the  tool. 

ACTION. — The  machine  is  driven  by  two  belts  passing 
over  pulleys,  /.  As  the  motion  is  reversed  at  every  stroke, 
one  of  the  belts  is  open  and  the  other  crossed,  as  previously 
explained. 

The  gearing  is  also  arranged  so  that  the  backward 
movement  of  the  table  after  the  cut  is  much  quicker  than 
the  forward  motion,  when  the  tool  is  working.  This  is  to 
save  time.  The  action  of  the  machine  is  automatic  both  as 
to  motion  of  table  and  feed,  and  can  be  set  to  any  length  of 
stroke.  At  the  end  of  the  forward  travel  of  the  table  a  pro- 
jecting arm  on  it  moves  a  lever,  and  this  shifts  the  belts  on 
the  pulleys,  bringing  the  reversing-belt  into  action.  At  the 
end  of  the  backward  motion  of  the  table  the  feed  is  brought 
into  action,  and  the  tool  prepared  for  its  next  cut.  To  pre- 
vent breaking  the  cutting  edge  of  the  tool  by  dragging  it 
over  the  cut  in  the  backward  motion  of  the  table,  the  tool- 
holder  is  hinged  so  that  it  allows  the  tool  to  rotate  in  the 
direction  of  the  return  stroke,  but  holds  it  firmly  against 
rotation  in  the  opposite  direction.  The  same  principle  will 
be  found  later  in  the  rifling-tool. 

92.  The  Shaper — Parts— Action. 

There  are  certain  objections  to  the  planer  which  have 
led  to  the  introduction  of  a  modified  form  of  the  machine 
called  the  shaper.  For  small  work,  or  for  short  strokes  of 
the  tool,  power  is  wasted  in  moving  the  heavy  bed  of  the 
planer,  and  when  it  is  necessary  to  stop  the  stroke  of  the 
tool  at  some  definite  point,  as  at  a  shoulder,  it  is  difficult  to 
do  this  with  the  planer  on  account  of  the  delay  in  shifting 
the  belts.  The  shaper  remedies  these  defects. 

PARTS. — It  consists  of  a  bed,  a  (Fig.  60),  along  which 
slides  a  head,  b.  This  head  carries  a  ram,  c,  upon  which  the 
cutting-tool  is  fixed.  This  ram  moves  backward  and  for- 
ward at  right  angles  to  the  bed,  and  this  transverse  motion 
is  given  by  a  link,  d,  attached  at  one  end  to  the  ram  and 
at  the  other  to  an  arm,  e,  upon  the  toothed  wheel/.  The 
work  is  supported  upon  the  tables  g  or  //,  as  the  sliding- 


I72  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

head  may  be  moved  to  any  position  along  the  bed ;  or  if 
the  work  is  too  long  for  either  table,  it  is  supported  at  each 
end  by  them,  i  is  an  arbor  or  shaft  attached  to  the  bed, 
and  intended  for  cylindrical  surfaces.  The  tables  g  and  h 


FIG.  60. 

can  be  adjusted  vertically  by  screws,  one  of  them  being 
shown  at  j. 

ACTION. — The  machine  is  driven  by  a  belt  on  the  speed- 
cone  k.  Motion  is  communicated  from  this  cone  to  a  back 
shaft  m  through  the  gear-wheel  m' .  On  this  back  shaft  is  a 
small  pinion  splined  to  the  shaft,  so  that  it  will  slide  freely 
along  the  latter  and  yet  turn  with  it.  The  toothed  wheel 
/"is  driven  by  this  pinion,  and  this  gives  motion  to  the  arm 
ey  and  this  to  the  link  d  and  ram  c.  A  feed-screw,  n,  is  con- 
nected with  the  sliding  head  b,  and  is  driven  by  the  toothed 
wheel  m"  on  the  back  shaft  m.  This  gears  into  a  pinion  on 
the  feed-screw,  and  by  means  of  proper  gears  any  feed  can 
be  given  to  the  sliding  head. 

By  this  arrangement  the  sliding  head  is  fed  along  the 
bed  a  a  certain  distance,  just  before  the  beginning  of  each 
stroke.  By  changing  the  point  of  attachment  of  the  link  d 
nearer  to  or  further  from  the  centre  of  ey  the  length  of  stroke 
of  the  ram  may  be  decreased  or  increased,  and  by  changing 


GUNS. 


173 


its  point  of  attachment  to  the  ram  the  position  of  the  tool 
may  be  regulated.  The  speed  is  varied  by  the  cones. 
There  is  also  a  very  ingenious  mechanical  device  invented 
by  Sir  Joseph  Whitworth  to  cause  a  slow  forward  motion 
of  the  tool  while  cutting,  and  a  quick  backward  motion. 

93.  The  Drill-press— Parts— Action. 

This  machine  is  used  for  making  cylindrical  holes  of 
comparatively  small  size.  For  large  sizes,  such  as  the  inte- 
rior of  tubes,  gun-hoops,  etc.,  a  boring-mill,  or  boring  lathe, 
is  used. 

PARTS. — The  principal  parts,  Fig.  61,  are  the  frame  a, 
which  supports  all  the  parts ;  the  table  b,  upon  which  the 
work  is  held  ;  the  speed-cone  c,  which  gives  motion  to  the 
drill  and  the  other  parts  of  the  machine  ;  the  spindle  d, 
which  holds  the  tool  e  ;  the  feed-screw/,  which  gives  a  ver- 


FIG.  61. 


tical  motion  to  the  drill-spindle  and  its  tool ;  the  feed-shaft 
g,  which  carries  at  its  lower  extremity  a  hand-wheel,  h,  and 


1/4  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

at  its  upper  end  a  pinion,  i-\  this  pinion  gears  into  a  toothed 
wheel,  k,  whose  hub  or  centre  forms  a  nut  through  which 
the  feed-screw  f  passes  ;  this  wheel  and  nut  are  held  in  a 
collar,  so  that  it  can  rotate  freely  but  cannot  change  its  po- 
sition vertically  ;  the  bevel  gears  II'  give  a  motion  of  rotation 
to  the  spindle  d. 

ACTION, — When  motion  is  communicated  to  the  speed- 
cone  c  by  a  belt,  it  drives  the  bevel  gear  /',  and  this  drives  /. 

The  hub  of  the  bevel  wheel  /  is  hollow,  and  the  drill- 
spindle  d  passes  through  it.  By  means  of  a  spline,  the 
spindle  can  slide  freely  through  the  hub  of  /,  but  is  com- 
pelled to  rotate  with  it  no  matter  what  its  position  verti- 
cally may  be.  The  work  rests  on  the  table  b,  and  the  tool 
e  is  in  contact  with  it.  As  the  drill  rotates,  the  tool  is 
pressed  down  upon  the  work  by  the  action  of  the  feed-screw 
/,  which  rests  upon  the  upper  end  of  the  drill-spindle  and  is 
connected  with  it  by  a  collar,  so  that  the  spindle  can  turn 
without  causing  rotation  of  the  feed-screw.  As  the  work 
progresses,  the  tool  is  fed  down  or  pressed  down  by  turning 
the  hand-wheel  /z,  which  causes  the  pinion  i  to  rotate,  and 
this  in  turn  rotates  the  toothed  wheel  k.  When  the  work 
is  finished,  a  reverse  motion  of  the  hand-wheel  h  causes  the 
feed-screw  /  to  rise,  carrying  with  it  the  drill-spindle  and 
drill. 

In  all  ordinary  drills  the  feed  is  both  automatic  and  by 
hand. 

94.  The  Milling-machine— Parts — Action. 

The  milling-machine  is  a  development  of  the  principle 
of  the  lathe,  and  is  used  for  forming  any  irregular  surface 
whose  elements  in  one  direction  are  parallel  to  a  plane  di- 
rector. In  this  machine  the  cutter  rotates,  while  the  work 
moves  at  right  angles  to  the  cutter  and  along  a  plane  sur- 
face. 

PARTS.— The  machine,  Fig.  62,  consists  of  the  bed  a, 
which  supports  a  frame,  #,  carrying  a  spindle  and  cone,  c, 
with  back  gear,  d,  as  in  the  lathe.  To  the  frame  is  attached 
a  horizontal  arm,  e,  for  the  support  of  the  outer  extremity  of 
the  axis  or  arbor  of  the  milling-tool/.  This  tool  is  fixed 


GUNS. 


175 


upon  an  axis  or  arbor,  one  end  of  which  is  supported  by 
what  may  be  called  the  live-centre,  and  the  other  end  by 
the  dead-centre  at  the  extremity  of  the  horizontal  arm  e. 
Below  the  cutter  is  a  table,  g,  which  moves  at  right  angles 


-rf 


FIG.  62. 

to  the  axis  of  the  milling-cutter.  This  table  is  capable  of 
adjustment  vertically  by  the  screw  k,  and  is  fed  trans- 
versely by  the  feed-screw  i  driven  by  the  worm-gear  j 
through  the  shaft  k  and  cone-pulleys  //'. 

ACTION. — Motion  is  communicated  to  the  cone-pulley  c 
by  a  belt,  and  this  causes  the  cutter  f  to  rotate.  Feed-motion 
is  also  communicated  to  the  table  g  from  the  cone-pulley  c 
through  gear  wheels  to  the  cone  /,  and  thence  by  a  belt  to 
/'.  From  I'  it  is  communicated  to  the  shaft  k  which  drives 
the  worm-wheel/,  and  this  drives  the  feed-screw  t. 

With  this  machine  it  is  not  necessary  to  have  a  constant 
velocity  ratio  between  the  motion  of  the  tool  and  that  of 
the  work,  and  hence  belts  instead  of  gearing  are  used  for 
the  feed.  Also,  since  the  cut  is  heavy  owing  to  the  large 


176  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

tool  employed,  a  slow  but  powerful  feed  is  required,  and 
this  is  obtained  with  the  worm-gear/.  It  is  evident  that 
the  profile  of  the  cutter  may  be  of  any  figure  within  wide 
limits.  Many  varieties  of  these  machines  are  used,  and  they 
are  largely  employed  in  the  manufacture  of  the  minor 
parts  of  small  arms. 


GUN-MANUFACTURE. 

95.  General  Description  of  Modern  Guns — Parts — Th§ 
Division  of  Operations. 

DESCRIPTION. — All  modern  high-power  guns  are  made 
of  steel,  and  are  composed  of  several  parts  united  to  form 
a  whole,  and  the  parts  are  so  arranged  as  best  to  support 
the  stresses  upon  them.  The  gun  is  therefore  called  a 
"  built-up  "  gun. 

PARTS. — The  principal  parts  are  (Fig.  63):  the  tube,  T> 


A 

A       T-  A 

.2  c 

~               D~*> 

''            ^5— 

J       ^—  =^- 

tt 

P   Tl         1       R 

FIG. 

63- 

1 

which  lorms  the  interior  of  the  gun  and  supports  the 
other  parts.  This  contains  the  powder-chamber,  P,  and  the 
rifling,  R.  The  jacket,  /,  is  the  next  larger  forging,  and 
rests  upon  the  exterior  of  the  tube,  carrying  in  rear  the 
base-ring  in  which  the  threads  of  the  breech-block  en- 
gage. The  hoops  may  be  divided  into  two  classes,  the  chase- 
hoops,  C  and  D,  and  the  reinforce  hoops,  A.  The  trunnion- 
hoop,  T ',  belongs  to  the  latter  class,  and  there  may  be  one 
or  more  layers  of  each  class  according  to  the  size  of  the  gun. 
The  hoops  are  arranged  to  break  joints  when  two  layers 
overlap,  or  to  lock  into  each  other  when  stiffness  is  required, 
as  in  the  chase-hoops.  The  interior  diameters  of  the  jacket 
and  hoops  are  less  than  the  corresponding  exterior  diame- 
ters of  the  tube  and  the  parts  enveloped.  This  difference 


GUNS.  177 

of  diameters  is  called  the  shrinkage,  and  its  amount,  and  the 
reason  for  using  it,  will  be  discussed  later.  These  cylinders 
are  put  in  place  by  heating  them  till  they  will  pass  over  the 
part  to  be  enveloped,  and  then  cooling  them  in  place. 

FORCINGS. — The  manufacture  of  the  forgings  and  their 
treatment  has  been  explained.  At  the  gun-factory  they  are 
finish-bored,  turned,  and  assembled  to  form  the  gun,  and 
after  assembling,  certain  operations  are  required  upon  the 
gun  itself  before  it  is  ready  for  service. 

DIVISION  OF  OPERATIONS.— The  mechanical  operations 
in  gun-building  are  therefore  naturally  divided  into : 

1.  Operations  before  assembling  ; 

2.  Operations  after  assembling. 

96.  Operations  before  Assembling — Tube — Warping — First  Boring: 
—Tool— Second  Boring— Tool. 

WARPING. — As  received  from  the  manufacturers,  the 
tube  is  liable  to  be  bent  or  warped,  due  to  the  oil-tempering. 

The  amount  of  this  warping  is  ascertained  by  mounting 
the  tube  in  a  lathe,  the  ends  being  centred  ;  and  as  the  tube 
rotates,  the  deflection  at  the  middle,  or  at  the  point  where  it 
is  greatest,  can  be  measured.  If  found  to  be  considerable, 
it  may  require  a  readjustment  of  the  axis  of  the  tube  in  the 
lathe,  or  it  may  be  so  great  as  to  cause  rejection  of  the  tube, 
though  this  latter  seldom  occurs. 

FIRST  BORING. — The  tube  is  bored  before  being  turned, 
in  order  that  when  turned  there  may  be  a  uniform  thickness 
of  metal  at  every  point  in  the  same  circumference.  The 
first  boring  is  done  with  a  tool  so  arranged  that  it  will  run 
straight.  This  is  necessary,  because  when  received  the 
bore  of  every  tube  is  irregular  to  some  extent,  and  the  tube 
is  generally  warped  or  bent  slightly.  The  bore  must  be  ex~ 
actly  parallel  to  the  axis  of  the  lathe,  as,  in  case  of  deviation 
from  this  line,  the  tool  may  run  so  far  to  one  side  as  to  spoil 
the  tube.  A  deviation  of  about  0.25  inch  in  a  length  of 
20  feet  would  reduce  the  thickness  of  metal  on  one  side  so 
much  that  the  tube  would  be  useless. 

TOOL.— The  tool  used  for  this  purpose  is  a  semi-cylinder 
of  cast  iron,  A,  Fig.  64,  carrying  a  cutting-tool  of  steel,  B,  \\\ 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

front.  This  semi-cylinder  exactly  fits  a  hole  in  the  bore  of 
the  tube,  which  hole  is  previously  bored  very  accurately 
with  a  small  lathe-tool.  The  tool  A  is  supported  by  a  long 


FIG.  64. 

bar,  C,  called  a  boring-bar,  which  is  pushed  forward  by  a 
feed-screw,  as  in  the  ordinary  lathe. 

The  tube  is  caused  to  rotate  while  the  tool  is  pushed  for- 
ward ;  and  since  the  semi-cylinder  A  accurately  fits  the  hole 
in  the  bore  at  starting,  and  is  constantly  forced  down  against 
it  by  the  presssure  of  the  cut  on  B,  it  produces  a  cylindri- 
cal surface  along  which  A  slides,  without  deviation.  The 
length  of  A,  being  about  three  times  the  diameter  of  the 
bore,  also  corrects  any  tendency  to  deviation. 

SECOND  BORING. — The  first  boring  gives  a  straight  hole, 
but  it  is  not  smooth  or  regular.  It  is  necessary  now  to  use 
a  tool  which  will  remedy  these  defects. 

TOOL. — The  tool  used  for  this  purpose  is  called  a  wood 
reamer.  It  consists,  Fig.  65,  of  a  flat  cast-iron  head,  A,  car- 


_XA_ J\ 

— —    -jlL.^i J 


FIG.  65. 

rying  two  cutters,  b  b,  so  that  a  cut  is  made  at  opposite  ex- 
tremities of  a  diameter.  DD  are  two  pieces  of  hard  wood 
bolted  to  the  cast-iron  head,  and  turned  to  a  diameter 
slightly  greater  than  that  of  the  hole  to  be  made  by  the  cut- 
ters bb.  This  packing  D,  guides  the  cutters,  and  keeps  them 
steady,  and  being  thoroughly  oiled  it  polishes  the  bore. 
The  cutters  are  slightly  wedge-shaped  or  conical,  so  that 


GUNS. 


179 


FIG.  ob. 


they  tend  always  to  move  towards  the  axis  of  the  hole 
already  bored.  By  having  two  cutters,  each 
of  them  does  one  half  the  work  of  a  single 
cutter,  and  hence  the  tool  travels  compara- 
tively rapidly  down  the  bore ;  and  from  this 
fact,  and  also  because  a  light  cut  is  taken, 
and  the  cutting-edge  of  the  tool  is  long,  so 
that  the  work  is  well  distributed,  it  follows 
that  the  wear  of  the  tool  is  slight,  and  the 
bore  very  smooth  and  uniform.  Fig.  66  illustrates  this,  be- 
ing exaggerated  to  show  the  principle. 

The  tool  is  supported  in  the  same  bar,  C,  and  fed  forward 
as  with  the  first  tool,  the  tube  rotating. 

97.  Boring   and   Turning   Lathes — Back   Eests— Bore   of  Tube- 
Turning. 

LATHES. — In  all  these  operations  the  tube  is  mounted  in 
a  boring  and  turning  lathe.  These  lathes  consist,  Fig.  67,  of 
the  bed  B,  made  very  strong  and  much  larger  than  is  the 
ordinary  lathe  ;  the  head-stock  and  cone-pulley  C\  the  face- 


FIG.  67. 

plate  F\  the  slide-rest  S,  carrying  a  turning-tool;  the  back 
rests  R  R,  forming  intermediate  supports  for  the  tube  T '; 
the  boring-bed  O,  supported  on  the  bed  proper,  B,  and  car- 
rying the  boring-bar  P  with  its  tool  Q ;  the  feed-screw  V, 
which  lies  inside  the  boring  bar  P\  and  the  gears  W,  by 
which  the  feed-screw  is  driven. 

Motion  is  communicated  to  all  the  parts  by  the  belt  X, 
acting  on  the  cone-pulley.  This  causes  the  tube  to  rotate, 
and  also  communicates  motion  to  a  long  shaft,  not  shown  in 
figure,  upon  the  end  of  which  is  the  lower  gear-wheel,  W". 
The  motion  is  transmitted  through  W  to  W,  and  thence  to 
the  feed-screw  V,  and  by  changing  the  gears  any  ratio  be- 
tween the  velocity  of  rotation  of  the  tube  and  that  of  trans- 


180  TEXTBOOK  OF  ORDNANCE  AND    GUNNERY. 

lation  of  the  tool  Q  can  be  obtained.  The  back  rests  R  R 
can  be  adjusted  to  any  diameter  of  forging,  and  the  boring- 
bar  moved  forward  or  backward.  It  is  necessary  that  there 
be  only  one  source  of  motion,  since  if  the  feed-screw  or  slide- 
rest  were  driven  independently  of  the  cone-pulley,  a  change 
in  speed  of  one  would  not  cause  a  corresponding  change  in 
the  others,  and  hence  damage  to  tools,  tube,  or  machine 
might  result. 

The  slide-rest  is  driven  by  a  second  feed-screw  not  shown. 

In  this  lathe,  the  work  may  be  turned  on  the  exterior 
while  boring  is  in  progress.  It  is  best,  however,  not  to 
make  a  heavy  cut  on  the  exterior  during  boring,  as  it  may 
cause  bending  of  the  tube  and  consequent  irregularity  of 
bore.  Each  lathe  is  supplied  with  an  oil-pump,  by  means  of 
which  a  stream  of  oil  is  forced  into  the  bore  while  the  work 
is  in  progress.  The  chips  or  cuttings  come  out  at  the  op- 
posite end  of  the  tube  from  that  at  which  the  tool  enters. 
The  same  machines  in  general  are  used  for  boring  and  turn- 
ing jackets  and  hoops,  with  some  slight  changes  necessitated 
by  the  difference  in  size  of  the  forgings. 

BORE  OF  TUBE. — Before  assembling,  the  tube  is  bored 
below  its  finished  size,  as  the  cooling  of  the  jacket  and  hoops 
causes  irregular  contraction  of  the  bore,  and  metal  enough 
must  be  left  to  remove  these  irregularities  and  give  a  uni- 
form bore. 

TURNING. — After  or  during  boring,  the  exterior. of  the 
tube  is  turned  to  the  proper  diameter.  The  exterior  of  the 
jacket  and  hoops  is  not  turned  before  assembling,  as  changes 
in  these  diameters  are  caused  by  the  shrinkage,  and  it  is 
preferable  to  finish  them  after  assembling. 

98.  Assembling— Furnace— Expansion— Cooling. 

The  parts  having  been  turned  and  bored  as  explained  are 
carefully  measured  to  see  that  their  dimensions  are  correct. 
A  variation  of  0.003  mch  is  allowed  from  prescribed  diam- 
eters. If  the  dimensions  are  correct,  the  parts  are  ready  for 
assembling. 

FURNACE. — The  jacket  is  first  placed  on  the  tube.  To 
do  this  the  jacket  must  be  expanded  sufficiently  to  allow  the 


GUNS. 


181 


tube  to  pass  readily  through  it.  As  a  general  rule,  an  ex- 
pansion of  0.004  inch  per  inch  of  diameter  is  sufficient. 
That  is,  if  the  interior  diameter  of  the  jacket  be  15.00  inches, 
it  is  to  be  expanded 

15.00  X  .004  =  0.06  inch, 

and  the  expanded  diameter  will  be  15.00  +  .06=  15.06 
inches. 

To  obtain  this  expansion  the  jacket  is  heated  in  a  furnace. 
This  furnace  consists  essentially  of  a  vertical  cylinder  of  cast 
or  wrought  iron  closed  completely  except  at  the  top,  where 
the  forging  is  introduced  and  removed.  This  cylinder  is 
surrounded  by  a  fire-box  so  arranged  that  the  heat  shall  be 
as  uniform  as  possible  at  all  points.  This  uniformity  of 
heating  is  essential  to  prevent  warping  of  the  forging  and 
consequent  difficulty  of  assembling.  The  forging  is  pro- 
tected from  direct  contact  with  the  fuel,  to  insure  uniformity 
of  heating,  and  also  to  prevent  dirt  from  collecting  on  it,  as 
this  would  be  difficult  to  remove. 

EXPANSION. — The  amount  of  expansion  has  been  stated. 
The  heat  necessary  to  obtain  this  expansion  varies  slightly 
with    different   forgings,    but    ordinarily   it 
does  not  exceed  600°  F.  LI 

The  requisite  expansion  is   determined  ^f 

by  noting  the  colors  which  form  on  the 
polished  surface  of  the  steel,  as  these  colors 
pass  through  a  regular  gradation,  from  pale 
yellow  to  purple,  blue,  and  black.  The 
latter  color  is  seldom  exceeded. 

Gauges  are  also  made  of  the  exact  diam- 
eter to  which  the  bore  should  expand.  When 
the  color  indicates  the  proper  expansion,  the 
gauges  are  tried,  and  when  they  will  enter 
the  bore,  the  requisite  expansion  has  been 
attained. 

ASSEMBLING. — The  furnace  door  is  now 
opened,  the  jacket  hoisted  vertically  out  of 
the  furnace  by  a  crane,  and  placed  on  a 
•casting,  as  shown  in  Fig.  68.  This  casting  stands  in  a  pit  of 


-TUBE. 


-JACKET. 


1 82  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


E 
J 


FIG.  69. 


sufficient  depth  to  contain  the  tube.     The  tube  is  lowered 
slowly  through  the  jacket  till  it  is  in  place. 

COOLING.  —  The  heated  forging  is  now 
cooled  by  the  application  of  water  as  follows: 
Fig.  69  shows  a  section  of  the  tube  of  8" 
gun  with  hot  jacket  in  place  ;  J  is  the  jacket, 
T  the  tube  resting  against  a  shoulder,  C,  in  the 
jacket ;  D  is  a  ring  formed  of  pipe  bent  into 
a  circle,  the  inside  being  perforated  with 
small  holes  about  f  inch  apart. 

This  pipe  is  placed  above  the  shoulder  C, 
so  that  the  jacket  in  cooling  may  contract  or 
"  draw  "  toward  this  shoulder,  and  hence  in- 
sure a  tight  joint  there.  A  current  of  water 
circulates  through  the  pipe,  and  issues  from 
the  small  holes  on  its  interior  against  the  hot 
jacket.  By  this  means  the  cooling  can  be 
readily  effected,  the  ring  being  gradually 
moved  upward,  toward  the  breech,  as  the 
cooling  progresses.  It  is  important  that  the  parts  below 
E  be  cooled  first,  as  otherwise  the  jacket  will  grip  at  E,  and 
on  cooling  and  contracting  longitudinally,  it  will  compress 
the  tube  in  this  direction,  and  produce  great  longitudinal 
strains.  The  same  process  applies  to  hoops,  the  water  being 
applied  first  at  the  joint  between  the  cooled  and  the  hot 
hoops,  in  order  to  cause  contraction  toward  the  joint,  and 
keep  the  latter  closed. 

99.  Operations  after  Assembling — Finish-boring — Rifling — Rifling- 
machine — Rifling-tool. 

FINISH  BORING. — The  gun  after  assembling  is  placed  in 
the  boring-lathe,  and  finish-bored  up  to  the  true  diameter. 
The  wood  reamer  is  used  for  the  final  boring.  The  powder- 
chamber,  and  the  slope  connecting  this  with  the  bore,  are 
also  finished. 

RIFLING. — The  next  operation  is  rifling,  or  cutting  the 
spiral  grooves  in  the  bore  for  giving  rotation  to  the  pro- 
jectile. This  operation  requires  a  special  machine  and  tool. 

RIFLING-MACHINE. — This  resembles  to  some  extent  the 


G  UNS. 


183 


boring  and  turning  lathe  already  described,  but  differs  in 
the  following  respects : 

1.  The  gun  does  not  rotate  ; 

2.  The  cutting-tool  has  a  motion  both  of  rotation  and  of 
translation. 


FIG.  70. 

Fig.  70  shows  the  outlines  of  the  rifling-machine.  The 
gun  is  supported  on  a  bed  as  for  boring,  Fig.  67,  and  the 
rifling-bar  m  is  supported  as  in  boring  the  tube. 

The  feed-screw  b  gives  the  motion  of  translation  to  the 
rifling-bar  m  and  tool  g. 

To  the  side  of  the  rifling-bed  is  bolted  a  table,  o,  which  is 
horizontal,  and  on  this  table  is  bolted  a  "  guide  bar"  e,  made 
of  flexible  steel,  and  whose  shape  is  that  of  the  developed 
groove  of  the  rifling.  A  toothed  wheel  or  gear,  c,  is  fixed  to 
the  rifling-bar,  and  a  toothed  rack,  d,  engages  with  this  gear. 
At  the  outer  end  of  the  rack  are  two  small  rollers,//',  em- 
bracing the  steel  guide-bar  e.  The  rifling-bar  m  is  free  to 
turn  about  its  axis  while  moving  forward. 

The  action  is  as  follows :  When  the  rifling-bar  is  driven 
forward  by  its  feed-screw  b,  it  carries  with  it  the  toothed 
rack  d. 

The  outer  end  of  this  rack  travels  along  the  guide-bar  ey 
and  as  the  roller /bears  against  this  guide-bar,  the  rack  is 
pushed  inward  or  to  the  left  in  the  figure.  This  causes  the 
gear  c  to  rotate  to  the  right,  carrying  the  rifling-bar  with  it, 
and  thus  the  rifling-tool  is  caused  to  cut  the  proper  groove 
in  the  gun. 

RIFLING-TOOL  (Fig.  71). — This  is  a  cylindrical  head,  c,  oi 
metal  accurately  fitting  the  bore.  Four  radial  arms,  d,  slide 
in  grooves  in  the  front  face  of  the  cylinder,  and  carry  the 
cutters  k  on  their  outer  ends. 


184  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  inner  ends  rest  on  a  wedge,  e,  which  has  a  sliding 
motion  parallel  to  the  axis  of  the  cylinder.  By  sliding  this 
wedge  forward  the  radial  arms  and  cutters  are  pushed  out, 
and  by  sliding  it  backward  they  are  pulled  in.  By  this 
means  the  depth  of  the  cut  or  feed  is  regulated. 


TUBE. 

,         

RIF 

.ING  BAR.        I 

e    I  —  F==yH^\ 

cm 

II1           e                   II     r 

; 

i  j 

1 

HJ1 

ri^kr^ 

CL"  IfU  /c 

FIG.  71. 

When  the  tool  reaches  the  end  of  the  groove  in  the  gun, 
the  projecting  end  of  the  sliding  wedge  strikes  a  rod,  r,  in 
the  bore,  and  the  cutters  are  thus  drawn  back,  which  pre- 
vents breaking  them  by  dragging  them  over  the  cut ;  the 
motion  of  the  machine  is  then  reversed  and  the  tool  drawn 
out  of  the  bore.  As  the  rifling-bar  and  tool  move  forward, 
a  stream  of  oil  is  forced  on  the  cutters  by  a  pump. 

Arriving  at  the  end  of  the  cut,  the  cutters  are  automati- 
cally withdrawn  as  explained  ;  and  as  the  motion  of  the 
rifling-machine  is  reversed  the  bar  and  tool  return,  being 
guided  in  their  return  motion  by  the  bearing  of  the  roller/', 
Fig.  70,  upon  the  outside  of  the  guide-bar.  The  sliding 
wedge  is  then  adjusted  for  the  next  cut,  and  pushed  out  to 
the  front,,  raising  the  cutters,  and  so  on  till  the  groove  is  fin- 
ished.  To  cut  the  next  groove,  the  rifling-bar  is  turned  in 
its  bearings  a  distance  equal  to  the  width  of  one  land  of  the 
rifling,  and  the  new  groove  cut  as  above  described. 

The  remaining  operations  are  finish-turning,  inserting  the 
breech-screw,  fitting  the,  mechanism,  marking,  and  weighing,  and 
are  not  different  from  the  ordinary  operations  of  a  machine- 
shop. 


GUNS.  185 


ELASTIC    STRENGTH    OF    GUNS. 

100.  Definitions— Case  Considered — Radial  Stress  and  Strain. 

DEFINITIONS. — In  the  following  discussion  stress  means 
the  force  acting  in  pounds  or  tons  per  square  inch,  and  strain 
the  effect  of  this  force ;  this  effect  being  either  extension  or 
compression,  and  expressed  in  inches  per  inch  of  length. 

Elastic  Strength. — The  elastic  strength  of  a  cylinder  or 
gun  is  the  greatest  stress  to  which  it  can  be  subjected 
without  straining  any  part  of  the  cylinder  or  gun  beyond  its 
elastic  limit. 

CASE  CONSIDERED. — To  show  the  stresses  acting  upon  a 
cylinder,  and  the  strains  produced  by  them,  let  us  consider 
the  case  of  a  single  cylinder,  closed  at  both  ends,  and  acted 
upon  by  an  interior  pressure  only,  the  exterior  pressure 
being  that  of  the  atmosphere,  and  consequently  so  small 
that  it  may  be  neglected.  This  case  corresponds  to  that  of 
a  gun  composed  of  a  single  piece  of  metal,  closed  at  one  end 
by  the  breech,  and  at  the  other  by  the  projectile,  and  acted 
on  by  the  pressure  of  the  powder-gas.  It  is  evident  that  a 
normal  stress  is  acting  upon  all  parts  of  the  interior  of  this 
cylinder,  including  the  ends. 

RADIAL  STRESS  AND  STRAIN. — Take  a  ring  of  this  cyl- 
inder, whose  length  is  unity,  Fig.  72,  and  consider  a  cube  of 
this  ring  whose  edges  are  unity. 

Let  p  represent  the  normal 
stress  upon  the  inner  surface  of 
this  cube.  Then  the  effect  of 
this  stress  is  to  compress  the 
cube  in  the  direction  of  the 
radius,  and  to  decrease  the  thick- 
ness of  the  wall  of  the  cylinder. 
It  also  increases  the  length  of 
the  radius.  Since  the  same  is 
true  for  every  unit-cube  into 
which  the  ring  may  be  divided,  FIG.  72. 

we  conclude : 

(i)  That  one  effect  of  an  interior  stress  upon  a  closed 


1 86 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


tube  is  to  strain  the  wall  of  the  tube  in  the  direction  of  the 
radius ; 

(2)  That  this  stress  decreases  the  thickness  of  the  walls 
of  the  tube,  and  increases  the  interior  radius. 

This  is  called  the  radial  stress,  and  its  accompanying- 
strain  is  the  radial  strain. 

It  must  remembered  that  for  the  particular  case  con- 
sidered the  effect  is  as  stated.  But  we  may  have  both  an 
interior  and  an  exterior  stress  acting  at  the  same  time,  or 
we  may  have  an  exterior  stress  acting  alone,  the  interior 
stress  being  zero. 

According  to  the  relative  values  of  the  stresses  acting- 
we  may  have  therefore  a  radial  strain  of  extension  or  of 
compression,  as  will  be  shown  later. 

101.  Tangential  Stress  and  Strain — Longitudinal  Stress  and  Strain 
— Conclusions. 

TANGENTIAL  STRESS  AND  STRAIN. — Consider  again  the 
same  ring  of  metal  as  before,  whose  length  is  unity,  and  take 
any  particular  unit  cube,  as  a,  Fig.  73. 

The  stress  p  acts  normal  to 
the  diametral  plane  be,  and  its 
effect  is  to  separate  the  cylinder 
into  two  halves  along  this  plane. 
Hence  the  edges  of  the  cube  a 
parallel  to  the  direction  of  the 
stress  or  normal  to  the  plane  be 
are  strained  by  this  stress,  and 
this  is  true  for  the  whole  cube; 
hence  the  effect  is  to  elongate 
the  cube  in  this  direction.  This 

is  called  the  tangential  or  circumferential  stress,  or  the 
hoop  tension,  and  it  produces  a  corresponding  strain.  Its 
amount  is  obtained  by  multiplying  the  intensity  of  the 
stress  by  the  area  over  which  it  acts.  The  intensity  is 
/>,  and  for  each  side  of  the  ring  the  area  over  which  it 
acts  is  r  X  I  =  r.  Hence  the  resultant  tangential  force 
is  pr.  This  force  is  resisted  by  the  elasticity  of  the  fibres, 
and  it  produces  a  corresponding  stress  in  these  fibres, 
which  at  any  point  is  represented  by  /.  Since  the 


.FIG.  73- 


GUNS.  ig/ 

same  may  be  shown  for  each  of  the  unit  cubes,  the  total 
effect  of  this  stress  is  to  strain  or  elongate  the  interior  cir- 
cumference of  the  cylinder  in  the  direction  of  the  tangent. 
This  also  increases  the  length  of  the  radius.  Hence  we 
conclude : 

(1)  That  another  effect  of  the  interior  stress  upon  a  closed 
tube  is  to  strain  the  wall  of  the  tube  in  the  direction  of  the 
tangent. 

(2)  That  the  stress  increases  the  interior  radius  of  the 
tube. 

As  in  the  case  of  the  radial  stress,  it  must  be  remembered 
that  this  stress  may  decrease  the  circumference  of  the  interior 
layer,  or  shorten  the  radius,  depending  upon  the  resultant 
of  the  forces  acting. 

It  appears  from  the  above  discussion  that  the  radius  is 
changed  by  both  the  radial  and  the  tangential  stresses,  and 
the  two  cases  must  not  be  confused. 

LONGITUDINAL  STRESS  AND  STRAIN. —  In  addition  to 
the  radial  and  tangential  stresses  acting  on  the  unit  cube, 
there  is  a  third  stress  due  to  the  pressures  on  the  ends  of 
the  cylinder.  This  stress  acts  parallel  to  the  axis  of  the 
cylinder,  and  its  effect  is  to  strain  the  elementary  cube  in 
the  direction  of  this  axis.  Since  this  is  true  for  each  cube, 
the  resultant  strain  is  an  elongation  of  the  tube  in  this  direc- 
tion. 

This  is  called  the  longitudinal  stress,  and  it  produces  a 
corresponding  strain. 

CONCLUSIONS. — If  we  follow  the  same  method  of  discus- 
sion for  the  case  of  an  exterior  and  an  interior  stress  acting 
at  the  same  time,  or  for  the  case  of  an  exterior  stress  acting 
alone,  the  interior  stress  being  zero,  similar  results  will  be 
obtained. 

Hence  we  conclude  in  general  that  when  a  single  cyl- 
inder is  acted  on  by  exterior  and  interior  stresses,  their  effect 
is  to  produce  in  the  cylinder : 

1.  A  radial  stress,/,  and  its  corresponding  strain; 

2.  A  tangential  stress,  /,  and  its  corresponding  strain; 

3.  A  longitudinal  stress,  q,  and  its  corresponding  strain ; 


1 88  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

and  that  all  these  stresses  exist  at  the  same  time  and  at 
every  point  of  the  cylinder. 

102.  Relations  between  Stresses  and  Strains  when  all  the  Forces 

are  Tensions — Application  to  Cube  in  Gun-cylinder. 
RELATIONS  BETWEEN  STESSES  AND  STRAINS. — Since  all 
the  stresses  /,  /,  and  q  exist  at  the  same  time,  and  each  pro- 
duces its  own  strain,  it  is  required  to  find  the  resultant  strain 
due  to  these  three  stresses  acting  together. 

For  this  purpose  it  is  more  simple  to  consider  at  first, 
three  stresses  of  the  same  kind. 

If  a  cubical  elastic  solid  be  acted  on  by  a  given  stress  in 
a  direction  normal  to  one  of  its  faces,  experiment  shows 
that  it  produces  a  corresponding  strain  in  that  direction, 

and  that  it  will  also  produce  con- 
trary strains  in  the  two  direc- 
tions at  right  angles  to  the  first, 
equal  to  one-third  the  first  strain. 
Thus,  Fig.  74,  if  the  force  /  act 
on  the  cube  in  the  direction 
shown,  it  will  elongate  the  edges 
aa,  bb,  etc.,  and  will  contract  the  edges  ac,  ab,  and  this  con- 
traction will  be  one  third  the  elongation  of  aa,  bb. 

This  law  holds  only  within  the  elastic  limit.  Consider 
the  general  case  of  a  cube  acted  on  by  the  three  stresses  X, 
F,  and  Z,  at  right  angles  to  the  faces  of  the  cube,  and  sup- 
pose these  stresses  to  be  tensions. 

Let  A  be  the  resultant  strain  in  the  direction  of  the  stress 

M,  that  in  the  direction  of  F; 
v,  that  in  the  direction  of  Z; 
E0  the  modulus  of  elasticity  of  the  cube. 
The  stress  X,  by  a  preceding  principle  (see  equation 
(169)),  produces  a  strain  in  its  own  direction  equal  to 


E 


The  stress  F  decreases  this  strain  by  the  amount 


GUNS. 


I89 


and  the  stress  Z  by  the  amount 

\_  Z 
3^0* 

Hence  the  total  strain  in  the  direction  of  X\s 


*.  =  TrUr----  . 


In  the  same  way  we  have  for  the  total  strains  in  the 
direction  of  Fand  Z 


*      Z\. 

~  3  ~~3'' 

i(7       X      Y\ 

=  -~\Z J. 

£  ' 


APPLICATION  TO  CUBE  IN  GUN-CYLINDER. — Referring 
now  to  the  unit  cube  in  the  gun-cylinder,  we  have  the  same 
case,  except  that  one  of  the  stresses  is  a  compression. 
Hence,  substituting  in  the  above  equations  /  for  X,  —  p  for 
F,  and  q  for  Z,  we  have 


3       3 


.     .     .     (170) 


In  these  equations  A  is  the  strain  in  the  direction  of  the 
circumference  or  tangent,  p  the  strain  in  the  direction  of 
the  radius,  and  v  the  strain  in  the  direction  of  the  axis  of 
the  cylinder,  due  to  the  action  of  the  three  forces  /,  t,  and  q 
at  any  point.  These  strains  may  be  extension  or  compres- 


1 90  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY, 

sion  according  to  the  relative  values  and  directions  of  the 
forces. 

103.  Lamp's  First  Law  Connecting  /,  /,  and  q. 

In  equations  (170)  the  values  of  A,  /*,  and  v  are  unknown, 
and  they  are  expressed  in  terms  of  /,  /,  and  q,  which  are  also 
unknown. 

Hence  in  order  to  find  the  values  of  A,  /*,  and  v  in  known 
terms  it  is  necessary  to  establish  certain  equations  of  condi- 
tion, by  means  of  which  /,  />,  and  q  may  be  replaced  by 
known  terms.  This  has  been  done  by  what  are  known  as 
Lame's  formulas,  from  the  name  of  the  distinguished  in- 
vestigator of  the  subject  of  the  elasticity  of  solid  bodies, 
M.  Lame. 

To  deduce  the  first  law  it  is  assumed  that  the  longitu- 
dinal stress  q  is  constant  throughout  the  cross-section  of 
the  cylinder. 

This  is  not  exactly  true,  but  the  results  obtained  upon 
this  hypothesis  are  sufficiently  exact  in  practice. 

Assume  the  last  of  equations  (170), 


v  — 


In  this  equation  q  is  constant  by  hypothesis,  and  the 
value  of  v  varies  only  with  /  and  p.  One  third  of  the  dif- 
ference of  these  quantities  is  the  only  variable  in  the  above 
equation  ;  and  since  /  and  /  vary  together  at  different  points, 

the  variations  in  the  value —  will  be  small,  and  may  be 

O 

neglected  in  comparison  with  q. 

Hence  we  may  assume  without  material  error  that  v  is 
constant  throughout  the  cross-section  of  the  cylinder. 

From  this  we  have 

t—p  =  $(q  —  vE0)  =  constant,      .     .     .     (171) 
or 

t—p  =  constant (172) 


GUNS. 


19- 


Th  eref  ore 


in  which  T0,  POJ  7",,  and  P,  are  the  values  of  /  and  p  at  the 
interior  and  exterior  of  the  cylinder  respectively. 

From  this  we  have  Lame's  First  Law : 

The  difference  between  the  tension  and  the  pressure  is  the 
same  at  all  points. 

104.  Lamp's  Second  Law. 

The  second  law,  or  second  equation  of  condition  for/,  /, 
and  q,  is  deduced  as  follows : 
In  Fig.  75 

Let  R^  be  the  interior  radius  of  the  cylinder ; 
RV  the  exterior  radius ; 
r,  the  radius  of  any  circle  of  the  section  ; 
r',  the  radius  of   a  circle  of 
the  section,  exterior  and 
near     to     that     whose 
radius  is  r\ 

p,  t,  and  q,  the  radial,  tangential,  and 
longitudinal  stresses, re- 
spectively, at  any  point 
of  the  circle  whose 
radius  is  r\ 
P0  and  T0,  the  values  of  /  and  t  for  'FIG.  75- 

the  interior  of  the  cylinder ; 
P,  and  r,,  the  values  of  /  and  /  for  the  exterior  of  the  cylia 

der; 

q,  constant  for  all  parts  of  the  cross-section ; 
£"„  the  modulus  of  elasticity. 

Consider  the  cylindrical  ring  whose  radii  are  r  and  r} 
and  whose  length  is  unity. 

The  interior  pressure  p,  as  previously  shown  in  the  dis- 
cussion of  tangential  stress,  produces  a  tangential  stress  on 
the  interior  of  the  ring  equal  to  pr. 

For  the  circle  whose  radius  is  r'  the  pressure  p  becomes 
/',  and  the  force  causing  tangential  stress  on  the  exterior  of 
the  ring  is  p'r1. 


I92  TEXT-  BOOK   OF  ORDNANCE  AND    GUNNERY. 

There,  is  therefore  a  difference  in  tension  between  the 
two  parts  of  the  ring  equal  to 


and  this  difference  of  tension  is  balanced  by  the  product  of 
the  thickness  of  the  ring  r'  —  r,  and  the  mean  stress  along 
bb'  ,  or  along  any  other  part  of  its  thickness. 

We  have  therefore  the  following  equation  for  the  whole 
ring,  since  the  tension  and  pressure  have  opposite  signs. 

2p'r>  _  2/r  =  _  2l(r>  _  r),  .     .     .     .     (i;4) 


r  being  the  mean  stress  throughout  the  thickness  of  the 
ring.     From  which 


(I75) 


Passing  to  the  limit  by  making  r'  =  r,  in  which  case  r 
becomes  /,  we  have 


limit  of  (—  r)r,=  r=  —t  ......     (177) 

Hence 


From  (171)  we  have 

*=/+3(?-  "£„)  ......     (179) 

Substituting  the  second  member  for  /  in  (178),  we  have 


Differentiating ;  /  and  r  being  variables, 

pdr  4-  rdp 


GUNS.  193 

Reducing, 


dr_  ___  dp_  _ 
~:=  -' 


Integrating, 


Substituting  the  value  of  /  +  3(0  —  r£0)  from  (179),  we 
have 

......    (184) 


or 

(t  +  pY  =  7=1  =  constant.    .          .     .     (185) 


From  which  we  can  write 


and  from  these  we  have  Lame's  Second  Law  : 

The  sum  of  the  tension  in  the  direction  of  the  circumference? 

and  of  the  pressure  in  the  direction  of  the  radius,  varies  inversely 

as  the  square  of  the  radius. 

Formulas  (172)  and  (185)  are  known  as  Lame's  formulas. 

105.  Curve  of  Stresses  in  a  Cylinder—  Discussion. 

Lame's  formulas  enable  us  to  determine  the  stresses  ex- 
isting- at  every  point  of  the  cross-section  of  a  cylinder  sub- 
jected to  the  action  of  exterior  and  interior  forces.  A  curve 
showing  the  relation  between  the  radii  and  the  stresses  for 
all  points  of  the  cross-section  is  called  a  curve  of  stress,  and 
is  thus  determined. 

Assume  equations  (173)  and  (186)  : 


•*=:(  7; 
t-p     =    T,-P,: 


-/     -    T.-P, 


194  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Combining  these  equations,  and  eliminating   .T,  ,  ro,and 
/,  we  obtain 


-     ,  ,.. 

R*  -  R*  AY  -  AY      r*' 

Combining  again  and  eliminating  Tl  ,  T0  ,  and  /,  we  have 


Rt'R.\P.  -  P.)  i 

p=~    R;  -  R:        &:  -  R:   ?•  •  (lk 

Since  q  is  assumed  constant  throughout  the  cross-section 
it  is  not  considered  in  this  discussion. 

Equations  (187)  and  (188)  give  the  values  of  /  and  /  at 
any  circumference  whose  radius  is  r.  From  these  equations 
we  can  construct  the  curves  of  stress.  To  illustrate,  take 
equation  (187). 

Differentiating,  we  have 


dr  R:  -  R:       r3* 

Differentiating  (189),  we  have 

&=6R>K;(-Xt'P-? ('9°) 

From  (187),  we  have  for  the  values  of  /  for  the  interior 
and  exterior  of  the  cylinder,  by  making  r  =  R0  and  r  —  Rl , 
respectively, 

7^o  —  po  ±   °3  it — y-  _  /> _? L _;     0     e     (191) 

7^ p    <L_  r>   \     »      i"      o  /  /T^O\ 

^  i  —  'o  TTi  r>  a    —  *  i  ~^^          D~a~.       •       •       \192) 

AJ   —  ^0  yv:,  —  KO 

Now  considering  the  two  forces  P0  and  /*, ,  we  may  have 
the  following  cases: 

3.  p.  <  p,' 

First.     P,  >  Pt. 


G  UNS. 


195 


Equation  (189)  shows  that  — -  <  o ;  hence  /  decreases 
algebraically  as  r  increases.  Equation  (190)  shows  that 
-j-:t  >  o ;  hence  the  curve  of  stress  is  concave  upwards. 

If  we  lay  off  values  of  r  along  the  axis  OX,  and  of  /  along 
OY,  the  resulting  curve  will  be  the 
curve  of  stress  for  the  particular 
stress  considered,  and  may  be  any 
one  of  the  curves  b,  d,  c,  a  in  Fig. 
76.  If  J"0  and  J1,  are  both  positive, 
we  have  curve  b,  which  is  the  gen- 
eral case.  If  T0  =  —  Tl ,  we  have 
curve  d.  If  7"0  —  o,  we  have  curve  c. 
If  T0  and  Tt  are  both  negative, 
we  have  curve  a. 

Second.     P0  =  P,. 

In  this  case 

dt^_        d^_ 

and  the  curve  of  stress  becomes  a 
right  line  parallel  to  the  axis  of  OX. 

Equation  (191)  shows  that  T0  <  o,  FIG.  76. 

and  hence  the  right  line  will  be  below  the  axis  of  OX,  as 
in  Fig.  77. 


FIG.  77. 


FIG.  78. 


I96 


TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 


Third.      /></>. 

In  this  case 


dt 


dr* 


hence  /  increases  algebraically  with  r,  and  the  curve  is 
convex  upwards.  Equation  (191)  shows  that  T0  <  o,  and 
hence  the  curve  will  be  as  in  Fig.  78. 

106.  Conclusion  from  Curves — Method  of  Strengthening  Cylinder. 
CONCLUSION. — Similar  results  will  be  obtained  by  dis- 
cussing equation  (188),  and  an  examination  of  all  the  curves 

thus  obtained  will  show  that  in  general  the  greatest  stresses 

are  at  the  interior  of  the  cylinder,  and  the  object  of  modern 

gun-construction  is  to  strengthen  this  interior  layer. 

METHOD  OF  STRENGTHENING  CYLINDER. — Take  a  gun 

composed  of  one  piece  of  metal,  such  as  the  old  cast-iron 
guns.  When  fired,  the  interior  pressure  is 
P9 ,  and  the  exterior  pressure  is  zero,  since 
the  pressure  of  the  air  may  be  neglected. 

Then  P0>Pt,  and  the  curve  of  tensions 
is  b,  Figs.  76  and  79.  If  P0  is  great,  the 
inner  layer  may  be  deformed  or  ruptured 
before  the  exterior  layers  are  brought  to 
their  limit  of  endurance.  Suppose,  how- 
FIG.  79.  ever,  that  before  firing  we  cause  a  pressure, 

P1 ,  to  act  upon  the  exterior  of  the  cylinder.     Then  we  have 

the  case  where  P0  <  Pl ,  and   the  state  of 

stress  in  the  cylinder  before  firing  is  as  in 

Figs.  78  and  80.     That  is,  all  the  layers 

are     compressed,   those    at    the    interior 

more  than  those  at  the  exterior. 

Now  when  the  gun  is  fired,  we  have 

the  condition  P0  >  Pl ,  and   the   curve   of 

tensions  would  be  b,  Fig.  79,  were  it  not 

that  we  have  already  a  curve  of  tensions,/ 

Fig.  80,  in  the  cylinder. 

Hence  the  new  curve  of  tensions  is  the  resultant  of  the 

two  curves  b  and/  or  AB,  Fig.  8:. 


GUNS. 


I97 


A 


That  is,  before  the  inner  layer  can  be  put  in  tension,  a 
force  must  be  exerted  sufficient  to  overcome  the  preliminary 
-or  initial  compression,  and  after  this  any 
excess  of  the  force  will  produce  tension. 
The  result  is  shown  in  Fig.  81.  A' B' 
is  the  curve  of  tensions,  supposing  no 
previous  stress  acting  on  the  cylinder. 
CD  is  the  curve  of  initial  compression ; 
AB  is  the  resultant  curve,  which  is  ob- 
tained by  taking  differences  of  ordi- 
nates,  and  is  the  curve  representing 
the  actual  tensions. 

This  method  is  called  the  method  of 
initial  compression,  and  is  now  universally  used  in  guri-con- 
struction. 

107.  Values  of  the  Strains  at  any  Point  in  a  Cylinder  in  Terms  of 
the  Radii  and  Pressures. 

The  general  laws  of  the  stresses  in  a  cylinder  have  been 
determined,  and  the  curves  of  stress  constructed.  The  ob- 
ject of  the  present  discussion  is  to  find  the  values  of  the 
strains  A,  yw,  and  v  at  any  point  in  a  cylinder  in  terms  of  the 
•exterior  and  interior  pressures  and  radii,  and  of  the  modulus 
j£0J  these  strains  being  within  the  elastic  limit  of  the  metal. 
For  this  purpose  assume  equations  (170) : 


FIG.  81. 


-- 


It  may  be  shown  analytically,  and  the  result  has  been 
proved  by  actual  experience  in  gun-building,  that  in  con- 
sidering the  resistance  of  the  cylinder  we  can  simplify  the 
problem  by  neglecting  the  longitudinal  force  q,  and  consid- 
ering at  first  only  the  forces  /  and  /,  and  afterwards  con- 
.sider  separately  the  force  q,  when  the  longitudinal  strength 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

of  the  gun  is  to  be  determined.  This  is  equivalent  to  mak- 
ing q  =  o  in  the  above  equations.  These  equations  then 
become 


Substitute  the  values  of  t  and  /  from  (187)  and  (188)  in 
(193),  and  we  have 


.  -     ,  4t,-        J_  . 

:      >  '         -   •    ~    • 


_  4R:x:(P,  -  Pt)  _L 

"  '  *  >  ' 


These  equations  are  general  and  give  the  values  of  the 
strains  A,  /*,  and  v  at  any  point  r  in  a  cylinder. 

To  find  the  values  of  the  strains  at  any  particular  point 
we  substitute  for  r  the  value  of  the  radius  at  that  point. 

Thus  for  the  interior  of  the  cylinder,  substitute  Rti  for  r,. 
and  for  the  exterior  Rl  for  r. 

108.  Maximum  Values  of  Strains  in  a  Cylinder. 

If  any  part  of  a  gun-cylinder  is  subjected  to  a  stress 
beyond  its  elastic  limit,  this  part  becomes  deformed. 

Hence  other  parts  will  be  called  upon  to  bear  stresses 
different  from  those  for  which  they  were  calculated,  and 
the  result  will  be  that  after  a  few  rounds  the  whole  structure 
may  be  deformed  or  destroyed.  We  then  use  the  following- 
principle,  which  is  the  foundation  of  the  modern  theory  of 
gun-construction  : 

No  fibre  of  any  cylinder  in  the  gun  must  be  strained,  under 
any  circumstances,  beyond  the  elastic  limit  of  the  metal  of  that 
cylinder. 


GUNS.  199 

From  this  principle  we  can  determine  the  maximum 
stress  to  which  a  cylinder  can  be  subjected. 

It  has  been  shown  that  the  inner  layer  of  a  cylinder  is 
subjected  to  the  greatest  stress.  Hence  if  this  layer  does 
not  pass  its  elastic  limit,  every  other  layer,  and  consequently 
the  cylinder  itself,  will  be  safe. 

The  strains  at  the  inner  layer  will  be  obtained  from  (194) 
and  (195)  by  making  r  —  A^0.  Considering  for  the  present 
only  A  and  j*,  since  v  is  constant,  we  have,  making  r  =  R^  , 


..> 

~p7^e7)£;          '       •    •    •    (I97) 
(4tf,2  -  2Ra')P,  -  2R,'Pl 

*=--  ^R?^}£T    "   •   •  (I98) 

These  are  any  strains  within  the  elastic  limit. 

Let  00  be  the  elastic  limit  of  the  cylinder  for  tension  ; 

P0  ,  the  elastic  limit  for  compression,  in  pounds  or 
tons  per  square  inch. 

Then,  by  equation  (169),  the  elongation  at  the   elastic 
limit  will  be 

A 

£,' 

and  the  compression  at  the  elastic  limit 


and,  by  the  principle  previously  stated,  these  are  the 
maximum  strains  that  can  be  allowed.  Since,  in  general,  A, 
is  extension  and  /*  compression,  A  and  ^  must  be  equal  to 

~-  and  -§-,  respectively,  at  the  limit.    If,  however,  A  becomes 

^0  ^0 

compression  and  /*  extension,  A  must  be  placed  equal  to 

a 

§-,  and  u  to  -^, 

^0  ^0 

ing  these  values, 


a 

§-,  and  u  to  -^,  as  will  be  seen  later.    We  have  then,  equat- 


200  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

.y.-2*.v. 


109.  Limiting  Interior  Pressures — Discussion. 

LIMITING  INTERIOR  PRESSURES. — Solving  (199)  and  (200) 
for  Pa ,  we  find  the  pressures  which  will  produce  the  strains 

A  =  -=?-  and  /*  =  ~-,  and  these  will  be  the  maximum  interior 

£„  A. 

pressures  which  the  cylinder  will  stand.     These  values  are 

,p«*.   °  P. — l— i'»    •     •     •     (201) 


?  -  2R: 


Po9  will  cause  the  inner  layer  of  the  cylinder  to  elongate 
till  it  reaches  the  elastic  limit  00,  and  Pop  will  cause  the 
inner  layer  to  be  compressed  radially  till  it  reaches  the 
elastic  limit  p0. 

These  values  of  P0&  and  Pop  will  differ,  and  the  smallei 
value  marks  the  limit  of  stress  to  which  the  cylinder  can  b( 
safely  subjected. 

For  instance,  if  Po9  <  Pop  ,  the  limit  #0  will  be  reached. 
while  that  for  compression  p0  will  not  be.  The  cylinder  has 
therefore  more  compressive  strength  than  can  be  used,  since 
if  we  increase  P0o  till  it  is  equal  to  Pop  ,  we  pass  the  limit  00  , 
which  is  contrary  to  the  principle  stated. 

DISCUSSION.  —  In  a  single  cylinder  the  most  common  case 
is  that  in  which  Pt  ,  the  exterior  pressure,  is  that  of  the 
atmosphere,  and  may  be  neglected.  Pl  is  therefore  zero,  and 
under  this  condition  equations  (201)  and  (202)  become 


Since  for  all  metals  used  in  gun-construction  #0  =  or  < 
P.,  P»o  will  always  be  less  than  PQP,  and  hence  it  alone  will 
be  considered. 


GUNS.  201 


(i)  Required  the  thickness  of  wall  necessary  to  resist  a 
given  interior  pressure  P00.  Solving  (203)  for  (JK,  —  Ro),  the 
thickness,  we  have 


-'     '  '  (205) 


(2)  To  show  the  relation  between  the  thickness  of  the 
cylinder  and  its  resistance,  we  have  from  (203) 


(206) 


Suppose  the  cylinder  to  be  one  calibre  thick.     Then 

K.-SX., 

and 

/U  =  *3«.. 

If  the  cylinder  be  of  infinite  thickness,  Rl  =  oo  ,  and 


which  shows  that  an  increase  in  thickness  from  one  calibre 
to  infinity,  increases  the  strength  of  the  cylinder  only  from 

.63^0  to  .7500- 

Hence  we  conclude  that  a  single  cylinder  is  not  materi- 
ally strengthened  by  increasing  its  thickness  beyond  one 
calibre,  and  also  that  the  greatest  possible  value  for  the 
interior  pressure  in  a  single  cylinder  without  initial  com- 
pression is  less  than 


110.  Limiting  Exterior  Pressures—  Thickness  of  Cylinder—  Exterior 
Strains. 

LIMITING  EXTERIOR  PRESSURES.  —  It  has  been  shown 
that,  in  order  to  strengthen  the  cylinder,  we  apply  an  exte- 
rior pressure  Plf  and  produce  a  compression  of  the  cylinder; 
this  compression  being  greatest  at  the  interior. 

What  is  the  limiting  value  of  this  exterior  pressure? 

Its  limiting  value  is  that  which  will  compress  the  inner 
layer  up  to  its  elastic  limit  ;  and  it  is  determined  as  follows: 


202  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  interior  pressure  being  zero,  or  P9  =  o,  the  strains  A 
and  JA  at  the  interior  become,  from  (197)  and  (198), 


(2O7) 


1^- (-S) 


The  first,  being  negative,  shows  that  the  inner  layer  is 
compressed  tangentially  ;  the  second,  being  positive,  that 
the  wall  of  the  cylinder  is  extended  in  a  radial  direction  or 
increased  in  thickness.  As  before,  the  limiting  compressive 
strain  is 


and  that  for  extension 


E.' 


and  the  values  of  A  and  //  must  not  exceed  these  respectively. 
Hence 


,  .  =  _n._. 

E.    (R;  -  R?)E,  ' 


.. 

-  £,  -      '       ' 


Solving  for  Pv  we  have 

,_(R^_R^P.. 
IP  2R          '    .....     V2O9; 


The  negative  sign  is  omitted  in  (209),  as  it  indicates  com 
pression  simply.     These  equations  are  useful  in  determining 
the  limiting  value  of  the  exterior  pressure  which  the  tube  or 
inner  cylinder  will  support,  when  we  are  considering  what 
pressure  Pl  can  be  applied  to  its  exterior  to  strengthen  it  ; 


G  UNS.  2O3 

and  since  PIP  is  generally  less  than  Pl9  ,  equation  (209)  only  is 
used. 

THICKNESS  OF  CYLINDER  TO  RESIST  EXTERNAL  PRES- 
SURE. —  From  equation  (209)  the  thickness  of  wall  of  cylinder 
necessary  to  resist  a  given  exterior  pressure  PIP  may  be 
obtained. 

Solving  it  for  Rt  —  R0  —  H'y  the  thickness,  we  have 


STRAIN  AT  EXTERIOR  OF  CYLINDER.  —  The  only  strain 
of  importance  at  the  exterior  of  the  cylinder  is  that  in  the 
direction  of  the  circumference,  or  A..  Referring  to  the  gen- 
eral value  for  it  at  any  point  r,  equation  (194),  and  making 
r  =  R,  ,  we  have  for  its  value  at  the  exterior 


A  = 
When  P0  =  o, 

x  =    -«*•'+ 


a  contraction. 
When  PJ  =  o, 

*  =  (je«2f0je°')£» *     (2I4) 

an  extension. 

111.  Longitudinal  Strength. 

To  determine  this,  suppose  the  cylinder  closed  at  one 
end  by  the  breech,  and  at  the  other  end  by  the  projectile,  as 
in  a  gun.  The  total  pressure  acting  on  the  bottom  of  the 
cylinder  is  then 

The  area  of  cross-section  of  the  cylinder  is 


204  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

and  the  pressure  nR*PQ  is  resisted  by  the  elasticity  of  this 
cross-section.  Supposing  the  pressure  to  be  uniformly  dis- 
tributed, the  stress  per  unit  area  of  cross-section  is 

TtR^P,  P.R? 

3  ^  «   -      *  ' 


Substitute  in  the  third  of  equations  (170)  for  t  and/  their 
values  from  (187)  and  (188),  and  for  q  its  value  from  (215), 
and  we  have  for  the  value  of  the  strain  v  in  the  direction  of 
the  axis  of  the  cylinder, 


(2I6) 


The  maximum  value  of  this  strain  must  be  equal   to 

n 

•FT-  as  before,  hence 


_ 

-: 


Solving  for  P0,  we  have 

P0o  =  ^-^        0^2°         -L-i-     .     .     .     (217) 
If/>=o, 

pn*  = 


For  the  thickness  of  wall  necessary  to  resist  the  pressure 
P0  acting  parallel  to  the  axis,  we  have,  solving  (218)  for 


R,  -  R0  =  H"  =  R.(\/.P*  +o  3^°  -  i\       .     (219) 

This  discussion  applies  to  the  older  guns  made  of  a  single 
piece  of  metal.  With  modern  built-up  guns  the  breech- 
block is  in  an  outer  cylinder  or  jacket,  and  a  new  formula 
must  be  deduced  for  the  longitudinal  strength  in  such  a  gun. 


GUNS.  205 

112.  General  Principles  of  Built-up  Guns — Method  of  Applying  Ex- 
terior Pressure. 

GENERAL  PRINCIPLES. — It  has  been  stated,  in  discussing- 
the  resistance  of  a  single  cylinder,  that  it  may  be  strength- 
ened by  applying  a  force  /*,  to  the  exterior  of  the  cylinder. 
This  force,  as  shown,  produces  a  compression  of  all  the  lay- 
ers of  the  inner  cylinder,  the  interior  layer  being  compressed 
to  the  greatest  extent,  as  it  should  be,  since  it  is  extended 
more  than  any  other  layer  by  the  action  of  the  powder-gas. 

The  layers  of  the  cylinder  being  thus  subjected  to  tan- 
gential compression,  this  compression  must  first  be  over- 
come before  the  inner  layers  can  be  brought  to  a  state  of 
tension.  Hence  part  of  the  powder-pressure  is  exerted  to 
bring  the  inner  layers  to  a  neutral  state  of  strain,  and  any 
excess  of  pressure  over  that  required  for  this  purpose  will 
cause  tension  in  the  inner  layers.  It  is  evident,  however, 
that  since  the  cylinder  will  safely  support  a  certain  interior 
pressure  PQ0  or  Pop  without  this  preliminary  compression,  it 
will  support  a  much  greater  interior  pressure  with  the  aid 
of  this  compression. 

METHOD  OF  APPLYING  EXTERIOR  PRESSURES.  —  The 
method  of  applying  this  exterior  pressure  is  by  placing  over 
the  inner  cylinder  an  exterior  one,  whose  interior  diameter 
is  slightly  less  than  the  exterior  diameter  of  the  inner  cylin- 
der. The  exterior  cylinder  is  applied  as  has  been  explained 
in  Gun-construction.  Upon  cooling  it  contracts  upon  the 
inner  cylinder,  and  if  the  difference  of  diameters  is  properly 
regulated  it  will  produce  the  required  pressure. 

It  is  evident,  however,  that  in  compressing  and  strength- 
ening the  inner  cylinder,  the  outer  cylinder  is  itself  extended 
and  weakened  ;  but  this  extension  or  weakening  of  the  outer 
cylinder,  when  properly  regulated,  can  be  supported  with- 
out damage  to  the  structure. 

According  to  Lame's  second  law  the  sum  of  the  tension 
and  pressure  varies  inversely  as  the  square  of  the  radius. 
Hence  a  value  of  (T0  +  P0)  which  would  be  large  at  the 
interior  would  be  very  much  diminished  at  the  radius  ^,. 
This  principle  is  applied  to  any  number  of  cylinders  placed 
one  over  the  other.  The  differences  of  diameters  of  any 


206 


TEX 'T- BOOK  OF  ORDNANCE  AND    GUNNERY. 


two  adjacent  cylinders  is  called  "  the  shrinkage,"  the  re- 
sulting gun  a  built-up  gun,  and  the  cylinder  a  compound 
cylinder. 

113.  Calculations  for   Compound  Cylinder — States   Considered  — 

Nomenclature. 

CALCULATIONS. — Suppose  the  cylinders  assembled  with 
the  proper  shrinkage.  It  is  required — 

1.  To   calculate  the   maximum   resistance   of  the  com- 
pound cylinder ; 

2.  To  calculate  the  shrinkage,  so  that  when  assembled 
the  pressure  exerted  by  the  exterior  upon  the  interior  cyl- 
inders shall  be  such  as  to  give  to  the  compound  cylinder  its 
maximum  resistance. 

STATES  OF  CYLINDER. — When  the  powder-pressure  is 
acting,  the  cylinder  is  said  to  be  "in  action;"  when  the 
powder-pressure  ceases  to  act,  the  cylinder  is  "  at  rest."  It 
is  evident,  however,  that  the  system  is  not  free  from  stress 
when  at  rest,  owing  to  the  shrinkage ;  and  it  is  necessary  to 
consider  the  stresses  both  in  action  and  at  rest,  as  will  be 
seen  later. 

NOMENCLATURE.— For  simplicity  of  discussion,  consider 
that  the  compound  cylinder  is  made  up  of  two  cylinders 

only.  The  inner  cylinder  will  be 
designated  as  the  tube,  and  the 
exterior  as  the  jacket. 

In  Fig.  82  let 

R0,  Rlt  R^  be  the  radii  of  the  inte- 
rior, middle,  and  ex- 
terior surfaces  of  the 
cylinders,  Rl  being 
the  radius  of  the  sur- 
face of  contact  be- 
tween the  tube  and 
jacket ; 

/*0,  Plt  P,,  the  normal  pressures  at 
the  interior,  middle,  and  exterior  surfaces,  re- 
spectively, when  the  system  is  in  action ; 
A » A >  A »  variations  in  />0,/>1,/>a,  produced  by  any  cause 


FIG.  82. 


GUNS.  207 

whatever,  such  as   a  change  from  a   state   of 
action  to  that  of  rest  ; 
#0,  Blt  elastic  limits  of  tube  and  jacket,  respectively,  for 

tension  ; 

p0,  plf  same  for  compression; 

£0,  £„  moduli  of  elasticity  of  tube  and  jacket  respec- 
tively. These  are  generally  assumed  as  equal, 
hence  £0  =  E^  ; 

/Y,  the  normal  pressure  acting  at  the  surface  of  con- 
tact of  the  two  cylinders  when  the  system  is  at 
rest. 

For  a  single  cylinder  the  radii  have  been  denoted  in  the 
previous  discussions  by  R^  and  Rl  ,  and  the  pressures  by  P0 
and  P,. 

As  a  general  rule,  if  n  denote  the  number  of  the  cylinder, 
counting  from  the  interior,  its  radii  and  pressures  are  n  —  i 
and  n,  for  the  interior  and  exterior  respectively.  Thus,  for 
the  fourth  cylinder  we  have  R3,  1?4,  P3,  and  P4,  and  by 
applying  this  rule  the  equations  deduced  for  two  cylin- 
ders may  be  applied  to  any  number. 

114.  Resistance  of  Compound  Cylinder  in  Action. 

In  the  case  of  a  compound  cylinder  in  action  the  tube 
is  acted  on  by  an  interior  pressure  P9  and  by  an  exterior 
pressure  /*.  The  jacket  is  acted  on  by  an  interior  pressure 
Pl  and  by  an  exterior  pressure  Pa,  which  is  that  of  the  at- 
mosphere, and  therefore  regarded  as  zero.  The  jacket  is 
therefore  a  single  cylinder  acted  on  by  an  interior  force,  Plt 
and  its  resistance  is  given  by  equation  (203). 

Making,  in  (203), 

P*9  —  *  if>     ^o  —  ^i  » 

*,  =  *;,     ».=  «„ 

we  write 


Pl9  being  alone  considered,  because,  as  previously  shown, 
it  is  always  less  than  Plf  .     (See  equations  (203),  (204).) 

This   pressure  Pl9  will   extend   the  inner   layer  of   the 


2O8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

jacket  to  its  elastic  limit,  and  hence  it  is  the  greatest 
pressure  which  can  be  safely  applied  to  the  interior  of  this 
cylinder. 

The  pressure  Pl9  just  found  also  acts  upon  the  exterior 
of  the  tube,  and  P0  acts  upon  the  interior.  Hence  we  have 
the  case,  already  discussed,  of  a  cylinder  acted  upon  by  two 
forces,  and  equations  (201)  and  (202)  apply,  viz., 


_oo       i 

*R?  +  2R: 

-^o>o+2^,* 

4*;  -  2R; 

The  smaller  value  must  be  selected,  and  this  value 
marks  the  limiting  pressure  which  the  tube,  and  conse- 
quently the  compound  cylinder,  will  safely  support. 

When  this  interior  pressure  acts,  it  raises  the  inner  layer 
of  the  tube  to  its  elastic  limit  for  tension  or  compression, 
according  as  P0o  or  Pop  is  the  less.  At  the  same  time  it 
produces  the  pressure  Pl9  at  the  surface  of  contact.  Hence 
when  the  maximum  interior  pressure  is  acting  it  raises  the 
inner  layers  of  both  cylinders  to  their  elastic  limits. 

Equation  (220)  is  solved  first,  since  it  contains  only  known 
quantities  in  the  second  member.  The  resulting  value,  Pl&, 
is  then  substituted  in  both  (221)  and  (222),  and  both  of  these 
equations  can  then  be  solved,  the  smaller  value  being  taken 
as  explained. 

-  Collecting  these  equations  for  convenience,  we  have  for 
calculating  the  maximum  pressures  which  a  compound 
cylinder  composed  of  a  tube  and  jacket  will  safely  support 
in  action 


..  , 

*  +  2R: 

.>.  +  2*.-/», 

-  •••••   (222} 


G  UNS.  209 

115.  Longitudinal  Strength  of  Compound  Cylinder. 

In  a  gun  composed  of  two  cylinders  the  jacket  carries 
the  breech-block,  in  order  to  free  the  tube  as  much  as  pos- 
sible from  longitudinal  stress. 

The  total  pressure  upon  the  breech-block  is,  as  before, 


This  acts  upon  the  area  of  cross-section  of  the  jacket, 
which  is  n(R*  —  R*}  ;  hence  the  stress  per  unit  area  of  this 
cross-section  is 


__  «  (  ,  v 

"  n(R?  -  R?}  ~  R?  -  R*'  ' 

The  values  of  t  and  /  from  (187)  and  (188)  become  for 
the  outer  cylinder,  by  making  the  following  changes  in  the 
nomenclature, 


/>  =  o,        R,  =  R,  ; 

' 

-' 

Substituting  these  values  of  /,  /,  and  q  in  the  third  of 
equations  (170),  we  have 


_  _ 

3(/?;-^)£, 

The  maximum  safe  longitudinal  strain  upon  the  jacket  is 

e 

-—-.     If  the  value  of  v  calculated  by  (226)  is  less  than  this, 

*h 

the  jacket  will  not  be  overstrained  longitudinally  by  P0.     If 
f\ 

greater  than  -~,  the  pressure  P0  must  be  reduced. 

•"i 

The  limiting  value  for  the  pressure  is  obtained,  as  before, 
by  placing 


2IO  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Solving  for  P0,  we  have 

3w  -  RW  +  2P«R? 

°~  3*." 

116.  The  System  at  Rest — Reasons  for  Considering  It— Variations 
of  Pressure. 

The  formulas  previously  deduced  give  the  maximum 
pressures  which  the  .compound  cylinder  will  safely  support 
in  action ;  and  in  order  that  these  pressures  may  exist,  the 
jacket  must  be  applied  by  shrinkage  upon  the  tube.  The 
pressure  thus  produced  on  the  tube  will  strengthen  it. 

It  may  be,  however,  that  this  pressure  which  is  applied 
to  the  exterior  of  the  tube  will  be  so  great  that  when 
the  powder-pressure  ceases  to  act  it  will  compress  the 
inner  layer  of  the  latter  to  such  an  extent  as  to  cause  this 
layer  to  pass  its  elastic  limit.  Thus  the  tube  may  be  injured 
by  the  exterior  force  which  is  applied  to  strengthen  it. 

It  follows,  therefore,  that  although  the  compound  cyl- 
inder would  support  certain  pressures  in  action  if  the  req- 
uisite exterior  pressure  could  be  applied,  it  may  be  im- 
possible to  apply  this  pressure  to  the  exterior  of  the  tube  at 
rest,  and  therefore,  before  we  can  determine  whether  equa- 
tions (220),  (221),  and  (222)  represent  allowable  pressures  in 
action,  it  is  necessary  to  consider  the  effects  of  the  pressure 
at  rest  upon  the  tube. 

When  the  powder-pressure  acts,  we  have  the  forces  P9 
at  the  interior  and  Pl  at  the  surface  of  contact  of  the  cyl- 
inders. 

These  can  be  calculated  by  (220),  (221),  and  (222). 

When  the  powder  pressure  ceases  to  act,  the  interior 
pressure  becomes  zero,  and  the  variation  of  pressure  at  the 
interior  is  from  -|-  P0  to  o.  This  difference  between  the 
pressure  in  action  and  at  rest  gives  the  variation  of  press- 
ure. Hence  for  the  interior  we  have 

A  =  0-P0,     or    p0  =  -P0 (228) 

This  is  further  evident  by  considering  that  the  algebraic 
sum  of  the  pressure  in  action  and  the  variation  of  pressure 
must  be  the  pressure  at  rest. 


GUNS.  211 

For  the  surface  of  contact  of  the  two  cylinders  the 
pressure  at  rest  is  P/  and  in  action  it  is  Pt-  hence  the  varia- 
tion of  pressure  /,  at  that  surface  is,  as  before, 

>»»•>/'->,  .......     (229) 

117.  Limiting  Value  of  Exterior  Pressure   on   Tube  —  System    at 

Rest. 

The  limiting  value  of  the  exterior  pressure  upon  the 
tube  for  the  state  of  rest  is  that  value  which  will  compress 
the  inner  layer  of  the  tube  to  its  elastic  limit,  and  it  is  given 
by  equation  (209). 


and  no  greater  pressure  than  this  can  be  allowed  to  exist  at 
the  exterior  surface  of  the  tube  at  rest. 

Now  the  pressure  actually  existing  at  this  surface  "at 
rest"  is,  from  (229), 

/>/«=£•+>,  ......     (230 

This  value  of  /y  depends  on  Plt  the  pressure  at  the  ex- 
terior of  the  tube  "  in  action,"  and  also  upon  plt  the  variation 
of  the  pressure  at  that  surface  in  passing  from  the  state  of 
action  to  that  of  rest.  It  is  necessary  therefore  to  calculate 
/y  by  (231)  and  compare  it  with  PIP,  the  maximum  admis- 
sible pressure  calculated  by  (230).  If  /Y  >  P^,  it  follows 
that  it  will  strain  the  tube  at  rest  beyond  its  elastic  limit, 
and  hence  it  cannot  be  allowed.  The  value  P1P  must  then 
be  adopted  in  place  of  P/  and  be  substituted  for  it  in  (231). 
This  substitution  in  (231)  will  produce  a  corresponding 
change  in  the  value  of  Plt  and  this  change  in  P,  will  also 
change  P0.  (See  equations  (220),  (221),  (222).)  On  the  other 
hand,  if  /y,  from  (231),  be  less  than  PIP  from  (230),  P,f  must 
be  used  and  not  P1P,  because  although  the  tube  will  support 
the  pressure  PIP  >  /y  at  rest,  if  this  value  of  PIP  be  sub- 
stituted for  /y  in  (231)  it  will  cause  an  increase  in  the  value 
of  P,  ,  the  pressure  on  the  exterior  in  action. 

But  it  has  been  shown  previously  that  the  value  of  Pl 
from  equation  (220)  represents  the  greatest  pressure  which 
the  jacket  will  endure  in  action  without  passing  its  elastic 
limit. 


212  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Hence  this  pressure  must  not  be  increased. 

We  are  therefore  limited  on  the  one  hand  to  the  value 
P1P  ,  equation  (230),  which  must  not  be  exceeded  at  rest,  and 
on  the  other  to  the  values  P0  and  Pt,  equations  (220),  (221), 
(222),  in  action  which  must  not  be  increased. 

118.  Calculation  of  pv  in  Equation  (231). 

In  order  to  calculate  Pt'  from  (231)  we  must  know  /,, 
since  '/>,  is  given  by  (220).  To  calculate  /,  we  proceed  as 
follows  : 

When  variations  of  pressure  occur  at  any  surface  they 
produce  corresponding  changes  in  the  dimensions  of  the  sur- 
face at  which  they  act,  and  these  changes  depend  directly 
upon  the  variations  of  pressure  which  cause  them.  The 
changes  of  dimensions  in  the  direction  of  the  circumference 
of  the  cylinder  are  the  greatest  (see  equations  (194)  and 
(195)  ),  and  hence  it  is  only  necessary  to  consider  these. 

For  the  jacket,  the  exterior  pressure  is  always  zero,  and 
the  variation  of  pressure  at  the  interior  is/,.  Equation  (197) 
gives  the  change  of  the  inner  layer  of  a  cylinder  in  the  direc- 
tion of  the  circumference  due  to  the  forces  P0  and  />,. 

In  the  present  case  /*,=/,,  and  Pl  =  o.  Also  R,  =  R^  , 
R0  =  Rl  ,£„  =  £,,  hence 


A  =        .  .. 

'          •       ' 


For  the  tube  we  have  the  variation  of  pressure  /,  acting 
upon  the  exterior  surface,  and  /0  upon  its  interior.  Equa- 
tion (212)  gives  the  tangential  change  at  the  exterior  of  a 
cylinder  due  to  the  two  forces  P0  and  Pr  To  adapt  it  to 
the  present  case  make 


Making  these  substitutions,  we  have 


Since  the  exterior  surface  of  the  tube  and  the  interior 
surface  of  the  jacket  are  in  contact,  they  form  virtually  but 


GUNS.  213 

one  surface,  and  whatever  change  occurs  in  one  will  occur 
also  in  the  other.  Hence  the  two  values  of  A  in  (232)  and 
(233)  are  equal. 

Equating  these  and  solving  for/x,  we  have,  since  JS9  =  £„ 


And  since,  from  (228), 


we  can  find  /,  in  terms  of  P0  from  234. 

119.  True  Value  of  P.. 

The  true  value  of  P9  is  that  which  is  safe  for  the  system 
both  in  action  and  at  rest. 

It  has  been  shown  that  if  Pf  <  P1P,  the  values  of  P0  given 
by  (221)  and  (222)  are  safe. 

If  /Y>  P1P,  these  values  are  not  safe  and  the  true  value 
of  P0  is  calculated  as  follows  : 

The  equation  expressing  the  limiting  value  for  the  exte- 
rior pressure  system  at  rest  is 


(235) 


in  which  the  value  of  Plf  is  obtained  from  equation  (230). 
Hence 

/>,  =  />»-*  .....     •     •    (236) 

Substituting  the  value  of  /t  from  (234),  in  which  /0  =  —  P0  , 
p—p    4-  ^°2(^'      '  R*}p<> 

lp^  ' 


The  equations  expressing  the  limiting  values  of  the  in- 
terior pressure  for  the  state  of  action  are  (221)  and  (222). 

Substituting  the  value  of  P,  from  (237)  in  (221)  and  (222) 
and  taking  the  smaller  value,  we  have  the  true  value  of  P0  , 
which  will  be  safe  both  in  action  and  at  rest,  since  it  has 
been  obtained  by  combining  two  equations  which  contain 
the  conditions  of  safety  both  for  action  and  for  rest. 


214  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  results  of  the  substitution  are 


/>.*= 


2R:}  - 


^    •    •    (A> 


-  2R?)  - 


F1*-™-      '      '      (B) 


Having  the  true  value  of  P0  from  (A)  or  (B),  we  find  the 
true  value  of  /,  from  (234),  and  this  value  of  pl  in  (235),  with 
the  value  of  P1P  from  (230),  will  give  the  true  value  of  Pr 

120.  Calculation  of  the  Shrinkage. 

Shrinkage  is  the  difference  of  diameters  of  two  adjacent 
cylinders.  This  is  called  the  actual  or  absolute  shrinkage. 
Dividing  the  absolute  shrinkage  by  the  diameter,  we  have 
the  shrinkage  per  unit  of  diameter,  or  the  relative  shrinkage. 

In  Fig  83  let 

OA  be  the  interior  radius 


of  tube, 


1  of  jacket, 


OB  the  exterior  radius 
OC  the  interior  radius 
OD  the  exterior  radius       { 
before  the  cylinders  are  assembled.     Then 

2BC  =  2(OB  —  OC) 

is  the   absolute  or  actual   shrinkage, 
and 


2BC  _  2(OB-  OC)  __ 

~2~OC  ~~  OC 


E 


FIG.  83. 


is  the  relative  shrinkage. 

When  the  cylinders  are  assembled, 
the  surface  of  contact  will  take  a  po- 
sition such  as  E  E  E.  The  jacket  will 
compress  the  exterior  of  the  tube  by 
the  amount  BE,  and  the  interior  of 
the  jacket  will  be  extended  by  the 
amount  CE,  and  we  have 

BE  +  C.  E  =  BC, 


GUNS. 


21$ 


By  this  compression  the  force  />/  is  exerted  upon  the 
exterior  of  the  tube  and  the  interior  of  the  jacket.  It  is 
required  to  find  BE  and  C£,  and  the  shrinkage  will  then  be 
known. 

BE 
CALCULATION.  —  The  value   —  -  is  the  compression  per 

L/  Ls 

unit  of  length  of  circumference,  or  of  radius,  of  the  exterior  of 
the  tube,  produced  by  the  force  P{.  This  relative  compres- 

BE 
sion  is  strictly  -  ,  since  OB  is  the  original  exterior  radius, 

but  the  error  is  so  slight  that  it  may  be  neglected.  This 
compression  is-given  by  equation  (213),  since  P9  =  o,  hence 


BE  , 

'oc  "' 


The  value  -       is  the  extension  of   the  interior  of  the 


jacket  per  unit  of  length  of  circumference,  or  of  radius, 
duced  by  the  force  /Y- 

It  is  given  by  equation  (199)  by  making 

R,  =  R*\    />=o; 
#,  =  *,;    E.  =  Ei; 

p.  =  /Y. 

Hence 

CE 


_ 

-          '          '  -•'  .....     (239) 


The  negative  sign  is  omitted  in  (238),  since  it  simply  indicates 
compression. 

Hence  denoting  the  relative  shrinkage  by  0,  we  have 

_  BE+CE  _         2R?(Rf  -  R^P,' 

$~-      oc      =  EO(R?  -  R:)(R;  -  R?y  • 

Steps.  —  The   different   steps  in   the   calculation   of   the 
shrinkage  may  be  thus  summarized  : 


2l6  TEXJ^-BOOK  OF  ORDNANCE  AND    GUNNERY. 

1.  Calculate  Pl9t  P0e  and  Pop  by  (220),  (221),  and  (222). 
Use  smaller  value  of  P0. 

2.  Calculate  P1P  from  (230)  and  /,  from  (234),  making  in 
the  latter  />0  —   —  P0 ,  the   value  obtained  from  (221)  and 

(222). 

3.  Find  /Y  from  (231),  and  compare  this  value  with  that 
of  P1P  obtained  from  (230). 

If  /Y  from  (231)  is  greater  than  P1P  from  (230),  steps  4,  5, 
and  6  will  be  as  follows  : 

4.  Calculate  Po9  and  Pop  from  A  and  B.     Take  smaller 
value. 

5.  Recalculate/,  from  (234),  making />0  =  —  P0 ,  the  value 
found  from  A  and  B. 

6.  Find  P1  from  (237),  using  PIP  from  (230). 

7.  Calculate  the  relative  shrinkage  by  (240).     The  value 
of  P{  to  be  used  in  (240)  must  correspond  to  the  adopted 
value  of  P0 ,  being  either  (Pl  +  A)  from  (231)  or  PIP  from  (230) 
according  as  P9  is  retained  as  originally  found  in  step  i  or 
is  changed  as  indicated  in  steps  3  and  4. 

8.  The   absolute  shrinkage  is  obtained  by  multiplying 
the  relative  shrinkage  by  the  interior  diameter  of  the  jacket. 
Hence  if  5  denote  the  absolute  shrinkage, 

S  =  0  X  2Rr 

9.  The  exterior  diameter  of  the  tube  should  then  be 

2^/  =  2^  +  5. (241) 

121.  Measurements  in  Gun-construction  —  Thickness  of  Wall  — 
Length  of  Bore. 

MEASUREMENTS.— The  value  of  the  shrinkage  having 
been  calculated  by  (240),  the  exterior  diameter  of  the  tube  is 
given  by  (241).  The  exterior  of  the  tube  is  then  turned  to 
this  diameter,  an  error  of  0.003  incn  only  being  allowed. 

After  turning,  the  exterior  diameters  are  measured  at 
every  inch  of  length  of  tube  ;  if  too  large,  they  are  reduced  ; 
if  too  small,  they  cannot  be  corrected,  except  by  using  a 
smaller  jacket.  Hence  it  is  important  not  to  turn  below 
size. 


GUNS. 


217 


The  interior  diameters  of  the  tube  are  also  measured  at 
each  inch  of  length. 

The  tube  and  jacket  are  now  assembled,  and,  when  cool, 
the  interior  diameters  of  the  tube  under  the  jacket  are 
again  measured. 

The  pressure  of  the  jacket  upon  the  tube  will  produce 
a  contraction  of  the  bore  of  the  latter,  and  this  contraction 
is  given  by  equation  (207),  making  P1  =  P/,  since  this  latter 
is  the  pressure  at  rest.  The  measured  contraction  should 
agree  with  the  calculated  value  ;  and  if  it  does,  we  have  a 
proof  of  the  accuracy  of  the  measurements,  and  of  the  cor- 
rectness of  the  formulas. 

The  agreement  is  generally  very  close. 

THICKNESS  OF  WALLS. — From  previous  calculations  it 
has  been  shown  that  there  is  very  little  gain  in  tangential 
resistance  by  increasing  the  thickness  of  the  cylinder  beyond 
one  calibre.  This  rule  is  generally  followed  in  modern  guns 
for  the  thickness  of  wall  over  the  powder-chamber. 

The  thickness  at  other  points  along  the  chase  is  obtained 
by  a  consideration  of  the  powder-pressures  at  the  different 
points,  and  these  are  given  by  the  pressure-curve,  wrhose 
construction  has  been  explained.  It  is  also  necessary  to  so 
adjust  the  thickness  of  the  different  parts,  that  the  weight  of 
the  gun  shall  not  exceed  the  limit  generally  allowed  for  the 
different  calibres,  and  that  the  axis  of  the  trunnions  or  the 
centre  of  gravity  of  the  gun  shall  be  at  a  distance  from  the 
breech,  equal  to  about  f  the  total  length  of  the  gun. 

The  weights  of  guns  are  as  follows,  nearly  : 

8-inch 14  tons 

lO-inch 28     " 

12-inch 52     " 

12-inch  mortar , 13     " 

In  general,  the  shape  of  the  chase  conforms  to  that  of 
the  pressure  curve,  and  the  resistance  at  different  sections 
along  the  gun  is  calculated  so  that  at  any  section  it  shall 
always  be  greater  than  the  powder-pressure  by  a  certain 
coefficient  or  factor  of  safety.  For  the  1 2-inch  gun  the 
elastic  resistance  is  about  24  tons  per  square  inch,  and  the 


2l8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

powder-pressure  16  tons,  at  the  chamber,  so  that  the  factor 
of  safety  is  f £  =  1.5. 

LENGTH  OF  GUN. — For  a  given  calibre,  charge  of  pow- 
der, weight  of  projectile,  etc.,  we  can  calculate  by  Sarrau's 
formulas  the  value  of  u  for  a  required  initial  velocity  V,  and 
may  so  adjust  the  elements  of  loading  that  the  maximum 
pressure  shall  be  constant  and  equal  to,  say,  15  tons  for  this 
velocity.  Generally  modern  guns  are  from  35  to  45  calibres 
long. 

122.  Wire  Guns. 

In  the  built-up  gun  it  has  been  shown  that  when  in  ac- 
tion, the  inner  layers  of  the  tube  and  jacket  are  strained  to 
their  elastic  limits  respectively.  None  of  the  other  fibres 
are  strained  up  to  that  limit,  and  hence  the  total  strength  of 
the  metal  is  not  utilized.  If  instead  of  two  cylinders  we  have 
four,  assembled  with  proper  shrinkage,  the  total  thickness 
of  the  gun  being  constant,  it  is  evident  that  the  inner  layers 
of  each  of  the  four  cylinders  would  be  strained  to  their 
elastic  limits  and  hence  more  of  the  total  strength  of  the 
metal  would  be  utilized.  As  the  number  of  cylinders  in- 
creases, the  strength  utilized  will  be  greater,  till  we  finally 
approach  the  limit  where  the  cylinders  are  infinitely  thin,  and 
the  whole  thickness  of  metal  in  each  is  strained  to  its  limit. 

Practical  reasons,  however,  prevent  the  carrying  out  of 
this  method,  because  the  longitudinal  strength  of  the  cylin- 
ders decreases  with  the  thickness;  the  expense  of  boring 
and  turning  the  cylinders  is  great,  and  it  would  be  impos- 
sible to  bore  and  turn  very  thin  cylinders  accurately. 

For  these  reasons,  it  has  been  proposed  to  substitute  wire, 
for  the  rings  or  hoops  of  the  built-up  gun.  This  wire  is 
wrapped  round  an  inner  tube  with  a  certain  tension,  so  that 
the  tube  is  compressed  initially  as  in  the  case  of  the  built-up 
gun,  and  the  wire  extended. 

The  advantages  claimed  for  the  wire  gun  are : 

i.  The  tension  of  the  layers  of  wire  can  be  so  regulated 
that  each  wire  will  be  strained  to  its  elastic  limit  when  the 
system  is  in  action,  and  we  approach  the  condition  of  in- 
finitely thin  cylinders. 


GUNS.  219 

2.  The  wire  being  very  small  in  section,  any  physical 
defects  can  be  detected,  and  hence  all  the  metal  in  the  gun 
will  be  sound. 

3.  A  high  elastic  limit  can  be  given  to  the  wire,  and 
hence  it  will  have  a  greater  tangential  strength  than  a  forged 
steel  hoop. 

4.  In  order  to  utilize  the  high  elastic  limit  of  the  wire,, 
the  tube  may  be  compressed  at  rest  beyond  its  elastic  limit. 

The  objections  are : 

1.  Compressing  the  inner  layer  of  the  tube  beyond  its 
elastic  limit  violates  the  fundamental  principle  of  modern 
gun-construction  ;  and  if  this  is  not  done,  the  wire  gun  can- 
not in  general  be  stronger  tangentially  than  the  built-up 
gun,  since  the  strength  of  the  tube  marks  the  limit  of  the 
strength  of  the  system. 

2.  The  coils  of  wire  have  no  longitudinal  strength,  and 
hence  the  longitudinal  strain  must  be  supported,  as  in  the 
built-up  gun,  by  a  jacket,  and  the  attachment  of  this  jacket 
to  the  tube  presents  difficulties. 

3.  The  wire  gun  is  not  as  stiff  longitudinally  as  the  built- 
up  gun,  since  the  wire  does  not  support  the  tube  so  firmly 
as  the  hoops.    This  is  a  question  of  importance  with  modern 
long  guns. 

123.  Description  of  Wire  Guns— Woodbridge— Crozier— Brown 
Segmental. 

WOODBRIDGE  (Fig.  84). — This  gun  consists  of  an  inner 
tube,  /,  wrapped  with  wire  as  shown.  Over  the  rear  part 
of  the  tube  is  a  jacket,  j,  made  of  longitudinal  steel  bars  of 
wedge-shaped  cross-section. 

This  jacket  is  wrapped  with  the  wire  w,  under  such 
tension  as  to  strongly  compress  the  inner  tube  at  rest. 
The  longitudinal  thrust  is  transmitted  to  the  jacket  as  fol- 
lows :  The  jacket  is  screwed  to  the  tube  in  rear ;  the  trun- 
nion-hoop t'  bears  against  a  thin  hoop  h,  and  this  against  a 
collar  c  screwed  to  the  jacket  in  front.  Hence  the  pull 
of  the  breech  block  in  rear  is  transmitted  to  the  rear 
of  the  jacket,  and  the  thrust  of  the  trunnions  to  the  front 
of  it. 


22O 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


The  calibre  of  the  gun  is  10  inches. 

CROZIER  (Fig.  85).  —  In 
this  gun  the  tube  is  com- 
pressed initially  beyond  its 
elastic  limit  by  the  wire. 

The  principal  features  are : 

1.  The  wire  on  the  chase 
is  covered  on  the  exterior  by 
thin  hoops,  put  on  with  very 
slight  shrinkage,  so  as  to  give 
stiffness,  and  protect  the  wire. 

2.  A  jacket  of  cast  iron  or 
cast  steel  is  used  for  cheap- 
ness,   to   carry    the    breech- 
block and  support  the  longi- 
tudinal strain.     It  is  put  on 
with  very  little  shrinkage,  the 
tangential    strength    of    the 
gun  depending  on  the  tube 
and  wire  alone. 

3.  The   jacket    and   tube 
are  connected,  and  the  mo- 
tion of  either  prevented,  by 
a  series  of  rings  or  steps,  a, 
abutting  against  each  other. 

BROWN  SEGMENTAL  (Fig. 
86). — In  this  gun  there  is  first, 
a  small  lining  tube,  a,  which 
extends  beyond  the  trun- 
nions. The  metal  of  this 
tube  has  a  high  elastic  limit, 
1 12,000  Ibs.  The  main  tube, 
b,  is  made  of  wedge-shaped 
steel  bars,  of  about  the 
same  elastic  limit.  This 
outer  tube  is  wrapped  with 
wire,  and  compressed  to  such 
an  extent  that  its  interior 


FIG.  84. 


FIG.  85. 


is  under  compression  even  in  action.     This  prevents  the 


GUNS.  221 

joints  betwsen  the  bars  from  opening.  The  jacket  is  light, 
and  is  not  in  contact  with  the  wire  except  at  the  trunnions 
and  breech.  The  figure  shows  the  method  of  attachment  of 

A 


A  FIG.  86. 

the  breech-block.  The  pull  of  the  block  at  the  breech  and 
the  thrust  of  the  trunnions  in  front  are  borne  by  the  jacket. 

Relative  motion  of  tube  and  jacket  is  prevented  by  the 
connection  in  rear. 

These  guns  have  been  made  and  tried  in  this  country. 
In  Europe  the  systems  of  Schultz,  Longridge,  Armstrong, 
and  others  have  been  tried. 

MEASUREMENTS. 

124.  Necessity  for — Measurements  Required— Standard  Comparator. 

NECESSITY  FOR. — In  a  modern  gun  it  has  been  shown 
that  the  stresses  and  shrinkages  are  functions  of  each  other. 
Hence,  if  the  correct  shrinkage  be  not  given  to  the  gun,  it 
will  not  properly  support  the  stress  to  which  it  is  subjected, 
and  may  be  either  strained  beyond  its  elastic  limit,  or  not 
strained  up  to  that  limit  according  to  the  actual  value  of  the 
shrinkage  as  given  in  construction.  After  these  shrinkages 
are  calculated  theoretically,  their  application  to  a  particular 
gun,  depends  on  the  accuracy  of  the  measurements  made  by 
the  inspector  during  construction.  Hence  the  necessity  for 
accurate  measuring  instruments,  and  skill  in  their  use. 

MEASUREMENTS  REQUIRED. — In  general  the  following 
measurements  are  required  in  gun-manufacture : 

1.  Interior  diameters  ; 

2.  Exterior  diameters  ; 

3.  Lengths; 

4.  Measurements  by  templets  and  gauges. 
STANDARD  COMPARATOR. — In  this  case,  as  in  all  others 

where  accuracy  is  required,  all  measurements  must  be  re- 
ferred to  a  common  standard.  This  standard  is  called  a 


222 


TEXT-BOOK  OF  ORDNAA^CE  AND    GUNNERY. 


"  comparator,"  and  its  general  principles  may  be  explained 
as  follows : 

A  stiff  bed  or  body,  a,  of  cast  iron,  Fig.  87,  rests  upon 
three  le veiling-screws  with  rounded  points  of  support. 


FIG.  87. 

In  this  bed  is  a  groove  or  recess,  c,  in  which  rests  a 
standard  bar  or  rod,  *•',  accurately  graduated  in  inches  and 
decimal  parts  of  an  inch.  On  top  of  the  bed  is  the  rib  d, 
which  forms  the  guide  for  the  heads  e,f,  and  g,  which  slide 
along  it.  These  heads  can  be  fixed  by  clamp-screws  in  any 
position  along  the  bed.  e  is  called  the  fixed  head, /the 
sliding  head,  and  g  the  auxiliary  head,  hh  are  two  sockets 
which  carry  steel  points,  and  these  points  can  be  adjusted 
lengthwise  in  the  sockets,  and  clamped  by  the  clamp-screws  ; 
i  is  a  microscope  reading  o.oooi  inch  ;  /£,  a  tangent  screw  con- 
necting/and^. 

Use.- — The  primary  object  of  this  instrument  is  to  lay  off 
exact  lengths.  To  do  this,  the  graduated  bar  being  in  its 
recess  c,  bring  the  ends  of  the  steel  points  h  h  in  contact. 
Then  adjust  the  graduated  bar  and  microscope,  till  the  zero- 
line  of  the  eyepiece  of  the  microscope  coincides  with  the 
zero  of  the  graduated  bar.  Clamp  the  fixed  head,  e,  and 
slide  the  sliding  and  auxiliary  heads,  till  the  microscope  is 
over  the  nearest  division  of  the  graduated  bar  correspond- 
ing to  the  length  to  be  measured. 

The  auxiliary  head  g  is  then  clamped,  and  the  sliding 
head  f  moved  by  the  tangent-screw  k  till  the  microscope 
reads  the  required  part  of  the  inch.  The  distance  between 
the  points  h  h  will  then  be  the  length  required. 

125.  Measurement  of  Interior  Diameters  of  Short  Hoops— Meas- 
uring-points— Use. 
The  interior  diameters  to  be  measured  may  be — 


G  UNS. 


223 


1.  Those  of  a  comparatively  short  hoop  ; 

2.  Those  of  a  long  hoop  or  tube. 

In  the  first  case,  when  the  length  of  the  hoop  is  such  that 
all  parts  of  it  can  be  reached  by  hand,  measuring  points  or 
rods  are  used. 

MEASURING-POINTS. — For  diameters  from  two  to  ten 
inches,  the  points  are  made  of  steel,  and  consist  of  a  fixed 
point,  a  (Fig.  88),  and  a  micrometer-point,  b.  The  fixed  point 


.,* 


FIG.  88. 

varies  in  length  according  to  the  diameter  to  be  measured, 
there  being  a  number  of  them.  Each  one  is  threaded  at  the 
end,  c,  and  the  micrometer-point  screws  on  this  thread  by 
the  corresponding  thread,  c' .  The  screw  d  of  the  microme- 
ter is  accurately  cut,  so  that  one  turn  of  the  head  e  cor- 
responds to  a  certain  decimal  part  of  one  inch,  generally 
0.025.  The  circle /is  then  graduated  to  read  o.ooi  inch. 

For  diameters  beyond  10  inches,  the  heat  of  the  hand  is 
found  to  affect  the  measurements,  as  it  causes  considerable 
expansion  in  a  long  steel  rod.  The  rod,  also,  if  made  suffi- 
ciently light  to  be  readily  handled,  would  lack  stiffness. 
For  these  reasons  the  measuring-points  for  larger  diameters 
are  made  as  follows  :  a  (Fig.  89)  is  a  holder  of  wood,  bored 


FIG.  89. 


out  in  the  middle,  b,  for  the  reception  of  the  fixed  and  mi- 
crometer points  c  and  d.  Metal  ferrules,  e  and/,  of  the  shape 
shown,  are  fitted  to  the  ends  of  the  holders,  and  are  pro- 
vided with  clamp-screws,  g,  to  clamp  the  points  c  and  d. 


224  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

These  points  are  essentially  the  same  as  before,  the  only 
difference  being  that  the  lengths  of  the  holders  vary,  and 
the  same  points  c  and  d  are  fitted  to  different  holders. 

USE. — Suppose  a  given  diameter,  say  12.50  inches,  is  to 
be  measured.  The  standard  comparator  is  first  set  to  12.50 
inches,  as  just  explained.  A  holder  of  proper  length  is  then 
selected,  and  the  points  c  and  d  fixed  in  it.  The  end  of  the 
fixed  point  c  has  an  adjustment  by  which,  having  set  the 
micrometer-point  at  zero,  the  length  of  the  whole  rod  can 
be  altered  till  it  is  exactly  12.50  inches.  The  interior  diam- 
eter of  the  hoop  can  now  be  measured,  and  the  differences, 
if  any,  in  thousandths  of  an  inch,  read  off  on  the  micrometer- 
scale  on  the  point  d.  There  are  also  other  methods  of  ad- 
justing the  rod. 

126.  Measurement  of  Interior  Diameters  of  Long  Tubes — The  Star 

Gauge — Setting  the  Star  Gauge. 

THE  STAR  GAUGE. — In  the  case  of  long  tubes,  all  parts 
of  which  are  not  readily  accessible,  some  means  must  be 
adopted  of  making  the  measurements  at  a  distance  from 
the  operator.  The  instrument  used  for  this  purpose  is  called 
a  "  star  gauge."  Its  principal  parts  (Fig.  90)  are  a  long  hol- 


FIG.  90. 

low  brass  rod,  a,  called  the  staff,  to  which  are  attached  the 
head,  £,  and  the  handle,  c. 

The  figure  and  description  are  intended  to  give  only 
a  general  idea  of  the  instrument,  and  are  not  accurate  in 
details,  as  the  instrument  is  too  complicated  to  be  fully 
described  here. 

The  head  b  has  three  or  more  sockets,  d,  which  are 
pressed  inward  upon  the  cone  g  by  spiral  springs,  not 
shown  in  the  figure.  Into  these  sockets  are  screwed  the 


GUNS.  225 

star-gauge  points  e.  There  are  generally  three  of  these, 
120°  apart,  varying  in  length,  for  the  different  calibres  to  be 
measured,  so  that  by  screwing  the  proper  points  into  the 
sockets  d,  any  diameter  can  be  measured.  The  handle  c  is 
at  the  other  extremity  of  the  staff  a.  In  the  older  forms  of 
star  gauge  it  had  a  sliding  motion  along  the  staff.  With 
the  new  instruments  motion  is  given  by  a  micrometer- 
screw.  Extending  through  the  staff  is  a  square  steel  rod,/, 
united  at  one  end  to  the  handle  c,  and  terminating  at  the 
other  end  in  a  cone,  g.  This  cone  has  a  known  taper,  and  a 
forward  movement  of  one  inch  corresponds  to  a  certain 
definite  increase  in  its  diameter.  This  increase  is  marked 
on  a  scale  upon  the  handle. 

Use. — When  the  handle  c  is  pushed  forward,  the  cone  g 
also  moves  the  same  amount,  since  it  is  connected  with  the 
handle  by  the  steel  rod/.  When  the  cone  moves  forward, 
it  pushes  out  the  sockets  d,  resting  upon  its  surface,  and 
this  forward  motion  of  the  handle  and  cone  continues,  till 
the  points  e  come  in  contact  with  the  walls  of  the  bore  to 
be  measured.  The  amount  of  this  outward  movement  of 
the  points  can  then  be  read  on  the  scale  on  the  handle,  and 
by  comparing  this  with  the  original  position  of  the  points 
the  size  of  the  bore  becomes  known. 

SETTING  THE  STAR  GAUGE. — As  with  the  measuring- 
points  previously  described,  it  is  necessary  to  "  set "  the  star 
gauge  before  use ;  that  is,  to  establish  an  origin  or  datum  to 
which  all  measurements  are  referred.  Suppose  the  bore  to 
be  measured  is  10.00  inches  in  diameter.  Accompanying  the 
instrument  is  a  series  of  rings  very  accurately  bored  to  the 
different  sizes  likely  to  be  required  in  practice.  The  10.00- 
inch  ring  is  selected,  and  the  standard  comparator  set  to 
that  length,  a  measuring-point  adjusted  to  it,  and  the  ring 
then  tested  by  this  point  to  see  if  it  is  exactly  10.00  inches. 
If  not,  the  error  is  noted  and  corrected  for.  The  lo.oo-inch 
points  having  been  screwed  into  the  sockets  of  the  star 
gauge,  the  ring  is  held  so  that  when  the  handle  is  moved 
forward,  the  points  will  all  touch  the  ring.  While  the 
points  are  in  this  position,  the  handle  is  adjusted  so  that  the 
reading-  is  zero. 


220 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


The  ring  is  then  removed,  the  instrument  inserted  in  the 
bore,  and  the  readings  of  the  scale  taken  for  every  inch  of 
length  of  bore.  These  readings  are  added  to,  or  subtracted 
from,  the  original  diameter  of  the  ring,  according  as  they 
are  greater  or  less  than  zero,  and  the  results  give  the  true 
diameter  of  the  bore. 

127.  Exterior  Diameters— Calipers— Arm— Support — Action. 

The  instruments  used  for  measuring  exterior  diameters 
are  called  calipers.  One  form  consists,  Fig.  91,  of  the  arm 
a,  the  measuring-points  b,  c,  and  the  support  d. 


e— 


FIG.  91. 


ARM. — The  arm  a  is  made  of  steel  in  a  semicircular 
form,  and  as  light  as  possible  consistent  with  stiffness.  The 
arm  terminates  in  sockets,  e,  at  each  end,  which  are  provided 
with  clamp-screws  e' . 

To  increase  the  stiffness  of  the  arm  and  protect  it  from 
variations  of  temperature  in  use,  it  is  covered  with  wood,  /. 

The  measuring-points  b,  c  pass  through  the  sockets  e  in 
the  arm,  and  are  clamped  in  position  by  the  clamp-screws  e\ 
The  point  b  is  called  the  fixed  point,  as  it  does  not  change 
its  position  relatively  to  the  arm  when  once  clamped  ;  the 
point  c  is  the  measuring  or  micrometer  point,  and  having  been 


GUNS.  227 

clamped  in  the  socket  e,  its  extremity,  c' ,  is  capable  of  a 
small  motion  by  means  of  a  micrometer-screw,  whose  con- 
struction has  been  previously  explained.  This  point  carries 
a  scale,  s,  reading  to  thousandths.  The  points  when  in  posi- 
tion are  always  in  a  straight  line. 

The  arm  with  its  points  is  suspended  from  its  support,  d, 
by  the  hook  g  and  spiral  spring  k. 

SUPPORT. — The  support  of  the  calipers  consists  of  a 
standard,  k,  fixed  to  a  bar,  /.  This  bar  slides  longitudinally 
upon  a  base,  m.  The  standard  k  carries  a  rod,  n,  to  which 
the  spiral  spring  h  is  attached,  and  to  this  spring  the  hook^-. 
The  whole  support  rests  on  the  exterior  of  the  tube  to  be 
measured,  being  brought  parallel  to  the  axis  by  the  feet  oo, 
and  held  in  this  position  by  the  leather  strap  /,  which  is 
buckled  tightly  around  the  tube. 

ACTION. — Suppose  a  diameter  of  15.00  inches  is  to  be 
measured.  Set  the  standard  comparator  to  this  length,  and 
having  determined  from  it  the  length  of  a  measuring-point 
of  exactly  15.00  inches,  set  the  micrometer-point  c  at  zero, 
and  adjust  the  points  b  and  c  in  the  sockets  till  the  distance 
between  them  is  exactly  15.00  inches.  Raise  or  lower  the 
caliper-arm  till  the  points  b  and  c  are  slightly  above  a  hori- 
zontal plane  through  the  axis  of  the  tube.  The  bar  /  may 
then  be  moved  along  the  tube  parallel  to  its  axis,  sliding  on 
the  bed  m,  and  measurements  made  for  every  inch  of  length. 
The  bar  /  will  slide  for  a  length  of  12  inches.  The  leather 
strap  p  must  then  be  loosened,  the  whole  support  moved 
forward  this  distance,  and  the  strap  again  tightened,  when 
measurements  may  be  made  as  before,  till  the  whole  is  com- 
pleted. 

128.  Measurement  of  Lengths — Step  Gauge— Surface  Lengths. 

The  accurate  measurement  of  lengths  is  very  difficult  to 
make,  and  as  each  particular  case  requires  a  special  arrange- 
ment, only  general  ideas  can  be  given. 

STEP  GAUGE. — One  of  the  most  frequent  measurements 
required  is  the  length  of  the  recess  or  step,  ab,  in  a  hoop.  If 
this  be  too  short,  the  hoop  will  not  come  in  contact  with  the 
preceding  one  when  shrunk  on ;  and  if  too  long,  an  opening 


228 


TEXT- BOOK  OF  ORDNANCE   AND    GUNNERY. 


3 

C             ls..J   f     \ 

,,,,",,  "'"'  l''\'      ;        r  -    '-]    JL   £ 

s 

_J 

D  1 

7^ 

f—  a-  -i    ^ 

-^           HOOP. 

will  be  left  at  the  shoulder,  which  leaves  the  tube  unsup- 
ported. To  measure  this  length,  an  instrument  called  a  step 

gauge  is  used.  This  con- 
sists, Fig.  92,  of  a  steel  blade, 
c,  sliding  through  a  socket 
in  a  body,  d.  These  blades 
are  of  different  lengths,  cor- 
responding to  the  different 
hoops  to  be  measured.  On 
the  end  of  the  blade  is  fixed 
a  steel  templet,  /,  which  ex- 
FlG  2  actly  fits  the  shoulder  in  the 

hoop.       The   templet    being 

held  against  the  shoulder  b,  while  the  body  is  pressed  against 
the  face  of  the  hoop  at  et  the  length  can  be  read  off  on  the 
scale. 

SURFACE  LENGTHS. — In  each  shrinkage  operation,  the 
changes  in  diameter  and  length  due  to  that  operation  are 
measured.  The  changes  in  diameter  are  measured  with  the 
points,  star  gauge,  or  calipers. 

For  measuring  the  changes  in  length,  the  following  plan 
is  adopted : 

Two  holes  are  made  with  a  punch  in  the  exterior  surface 
of  the  tube  or  hoop,  and  their  exact  distance  apart  before 
shrinkage  measured  as  follows : 

An  instrument,  Fig.  93,  consisting  of  a  main  body,#,  car- 


iitil       i       Ifl       I 

O                  O                   0                   0                  0                   0 

FIG.  93. 

ries  a  fixed  head,  b,  and  two  movable  points,  c  and  d.  The 
pofnt  c  is  attached  to  a  sliding  head,  cf,  which  carries  a 
micrometer-screw,  e. 

g  is  an  extension-bar,  having  holes  at  intervals  of  0.25 
inch. 


GUNS.  229 

Accompanying  the  instrument  are  reference-bars,/,  which 
have  holes  in  them  exactly  one  inch  apart,  and  at  the  left 
end  one  inch  is  graduated  into  J,  -J,  {  inch. 

When  the  holes  are  punched  in  the  surface  of  the  hoop 
as  before  explained,  their  distance  apart  is  measured 
approximately  with  a  scale.  Suppose  this  distance  to  be 
18.40  inches. 

Move  the  point  d  along  the  extension-bar  g  till  it  will 
enter  the  1 8-inch  hole,  and  clamp  it,  the  screw  d'  passing 
into  one  of  the  holes  in  the  bar  g.  Place  the  instrument  on 
the  reference-bar/,  the  point  c  entering  the  J-inch  hole  in  it, 
and  the  point  d  resting  in  the  1 8-inch  hole.  The  distance 
between  the  points  c  and  d\s  now  18.50  inches. 

Fix  the  micrometer  e  at  zero,  and  move  the  points  b  and 
e  till  they  are  in  contact.  Now  place  the  instrument  on  the 
hoop  to  be  measured,  the  point  c  in  one  punch-mark  and  d 
in  the  other,  make  contact  again  with  e,  and  subtract  the 
reading  of  the  micrometer-scale  from  18.50  for  the  distance 
apart  of  the  holes. 

After  shrinkage  the  same  process  gives  the  distance 
apart  of  the  punch-marks;  and  the  difference  before  and 
after,  the  change  due  to  shrinkage. 

129.  General  Principles  of  Measurements — Touch — Interior  Diam- 
eters of  Short  Hoops. 

In  the  above  descriptions  all  the  complicated  details  of 
the  instruments  have  been  omitted,  and  only  the  general 
method  of  their  operation  and  use  given.  The  templet 
measurements  require  no  special  notice.  A  few  general 
principles  relating  to  the  method  of  using  these  instruments 
must  be  understood. 

TOUCH. — The  accuracy  of  all  measurements  with  these 
instruments  depends  upon  the  skill  of  the  operator,  and 
hence  practice  is  necessary  to  obtain  satisfactory  results. 
In  most  cases  the  sense  of  touch  is  relied  upon  to  determine 
when  proper  contact  of  the  measuring-points  with  the  sur- 
face to  be  measured,  is  obtained. 

Various  mechanical  devices,  such  as  electrical  indicators, 
etc.,  have  been  tried  to  determine  when  proper  contact  has 


230 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY 


been  obtained,  and  can  be  used  to  advantage  when  a  large 
amount  of  measuring  is  to  be  done. 

INTERIOR   DIAMETERS. — In   measuring   these   (Figs.   94 


S? 


FIG.  95. 

and  95),  the  hoop  is  placed  horizontally,  and  the  lower  fixed 
point  of  the  measuring-rod  a  is  held  by  the  operator  at  the 
point  whose  diameter  is  to  be  measured.  It  is  evident  from 
Fig.  95  that  the  diameter  is  the  shortest  line  from  a  to  b,  and 
hence  if  the  upper  point  of  the  measuring-rod  be  moved 
from  b  in  the  direction  of  the  arrows,  it  will  cease  to  touch 
the  surface  of  the  hoop. 

From  Fig.  94,  the  diameter  ab  is  the  longest  line  in  the 
cross-section;  and  if  the  point  be  moved  to  either  side  of  b, 
it  will  jam  against  the  surface  of  the  hoop.  Hence  in 
determining  an  interior  diameter  at  any  point  with  the 
measuring-rods,  hold  the  fixed  point  of  the  rod  firmly  against 
the  lower  surface  of  the  hoop  at  the  point  where  the  diam- 
eter is  required.  Move  the  micrometer-point  in  two  direc- 
tions at  right  angles  to  each  other,  one  along  the  axis  of  the 
hoop,  the  other  across  the  axis,  till  a  point  is  found  where 
contact  occurs  due  to  both  these  motions. 

The  reading  of  the  rod  will  give  the  diameter. 

130.  Interior  Diameters  of  Long  Hoops  —  Exterior  Diameters  — 
Vernier  Scale. 

INTERIOR  DIAMETERS  OF  LONG  HOOPS.— These  are  meas- 
ured with  the  star  gauge,  and  in  order  that  they  may  be 
correct  the  points  must  move  at  right  angles  to  the  axis  of 
the  bore. 

By  the  construction  of  the  instrument  these  points  must 
move  at  right  angles  to  the  staff  of  the  star  gauge,  and  hence 


GUNS. 


231 


it  becomes  necessary  that  the  staff  be  placed  accurately  in 
the  axis  of  the  bore.  For  this  purpose  the  gun  or  tube  is 
carefully  levelled,  and  various  supports  are  used  in  the  bore, 
which  insure  centering  of  the  star-gauge  staff.  Exterior 
rests  are  also  provided  to  support  that  part  of  the  staff  out- 
side the  bore. 

EXTERIOR  DIAMETERS. — In  the  measurement  of  exterior 
diameters,  the  same  principles  apply  as  to  interior  diameters. 
In  Fig.  96  the  diameter  c  is  the  longest  line  in  the  cross- 


• 


FIG.  96. 


FIG.  97. 


section,  and  the  shortest  line  in  the  longitudinal  section, 
Fig.  97.  Hence  the  fixed  point  of  the  calipers  is  held  at  a, 
and  the  measuring-point  b  moved  in  two  directions  at  right 
angles,  as  in  case  of  the  interior  diameters,  till  proper  con- 
tact is  made. 

VERNIER   SCALE. — A  very  useful  instrument  in  these 


FIG.  98. 


measurements  is  a  "vernier  scale,"  Fig.  98,  which  consists  of 
a  steel  blade,  a,  graduated  in  inches  and  decimal  divisions,  a 


232  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

fixed  jaw,  b,  a  mo\7able  jaw,  c,  and  an  auxiliary  jaw,  d,  with 
its  tangent  screw,  e.  The  principle  is  the  same  as  that  of  the 
standard  comparator,  lengths  being  measured  between  b 
and  c.  The  advantage  of  this  instrument  is  that  it  can  be 
carried  to  any  part  of  the  shops,  and  when  its  error  is 
determined  by  the  standard  comparator,  it  can  be  used  in 
place  of  the  latter  with  great  convenience.  Its  disadvantage 
is  that  it  is  affected  by  changes  of  temperature  when  carried 
to  different  places  in  the  shop,  and  when  handled. 

DESCRIPTION   OF   CANNON. 
1.  In  U.  5.  Service. 

131.  Classification — Hotchkiss  Mountain  Kifle. 

CLASSIFICATION. — Cannon  may  be  classified  according 
to  the  service  for  which  they  are  intended,  into  mountain, 
field,  siege,  or  sea-coast  guns ;  according  to  the  kind  of  fire 
they  deliver,  into  guns,  howitzers,  and  mortars ;  according  to 
the  kinds  of  projectiles  used,  into  smooth-bore  and  rifled  ; 
and  according  to  the  methods  of  loading,  into  muzzle-  and 
breech-loaders.  As  all  modern  guns  are  breech-loading 
rifles,  it  is  most  convenient  for  discussion  to  consider  them 
according  to  the  service  for  which  they  are  intended. 

Machine  and  rapid-fire  guns  will  be  considered  later. 

MOUNTAIN   GUNS. 

HOTCHKISS  MOUNTAIN  RIFLE.— This  is  the  only  gun  of 
this  class  in  service.  It  is  made  as  light  as  practicable,  so 
that  it  can  be  carried  on  the  back  of  a  mule,  its  weight  being 
1 1 6  Ibs.  Its  carriage  weighs  220  Ibs.,  and  two  men  can  pack, 
unpack,  and  mount  it. 

The  gun,  Fig.  99,  is  made  of  steel  in  a  single  forging,  the 


FIG.  99. 

trunnion-hoop  being  screwed  on.  The  calibre  is  1.65 
inches;  weight  of  shell  loaded  2  Ibs.  10  ozs.;  of  powder- 
charge,  5 1  ozs.  The  initial  velocity  is  1275  ft.-secs. 


GUNS. 


233 


Breech  Mechanism. — The  mechanism  is  a  simple  form  of 
the  Krupp.     It  consists  of  a  rectangular  steel  block,  b,  Fig. 


FIG.  100. 

ioo,  with  rounded  corners ;  its  front  face  being  at  right 
angles  to  the  axis  of  the  bore,  and  its  rear  face  slightly  in- 
clined to  that  axis. 

This  block  slides  transversely  in  a  recess  in  the  breech, 
and  when  withdrawn  leaves  the  breech  open  for  loading. 
It  is  locked  in  the  firing  position  by  a  cam,  c,  entering  a 
corresponding  recess  in  the  breech,  and  this  cam  is  operated, 
and  the  block  withdrawn  and  pushed  home,  by  the  lever- 
handle,  /.  e  is  the  extractor  for  withdrawing  the  empty 
cartridge-case.  It  is  a  prismatic  bolt,  sliding  in  a  groove  in 
the  upper  part  of  the  breech,  parallel  to  the  axis  of  the  bore, 
and  terminating  in  front  in  a  hook,  h.  A  tenon,  /,  on  the 
under  side  of  the  extractor,  fits  in  the  extractor-groove,  k, 
cut  in  the  top  of  the  breech-block.  This  groove  is  straight 
for  some  distance,  and  then  curves  quickly  to  the  rear. 
When  the  block  is  withdrawn  it  moves  in  guides  which  are 
parallel  to  its  rear  face,  and  which  consequently  give  it  a 
motion  such  that  the  extractor  is  at  first  gradually  with- 
drawn, thus  removing  the  empty  case  from  its  seat  in  the 
chamber. 

The  tenon  of  the  extractor  then  enters  the  inclined  part, 
a,  of  the  groove  in  the  block,  and  the  extractor,  with  the 


234 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


IOI 


cartridge-case,  is  drawn  quickly  backwards,  thus  ejecting 
the  case  to  the  rear.  The  motion  of  the  breech-block  is  ar- 
rested by  a  stop-bolt,  s,  which  is  screwed  through  the  upper 
part  of  the  breech,  and  enters  the  groove  r  on  the  top  of 
the  block. 

Ammunition. — The  ammunition  is  contained  in  a  metallic 
cartridge-case,  and  as  this  forms  a  gas-check,  no  accurate  fit 
of  the  parts  of  the  mechanism  is  required, 
and  the  breech-block  works  freely  in  its 
slot. 

The  charge  is  fired  with  an  ordinary 
friction  primer.  The  head  of  the  case 
is  formed  by  a  cup,  c,  inside,  Fig.  101, 
having  five  holes,  a,  in  it.  The  exterior 
is  strengthened  by  a  cup,  b,  having  five 
holes  corresponding  to  a  and  a  sheet- 
iron  disk,  d,  riveted  to  the  cups  and  case, 
and  having  a  central  hole,  v.  The  flame 
from  the  primer  passes  through  the  hole 
v,  and  thence  through  a  to  the  charge. 
The  gas-pressure  from  the  charge  forces  the  cups  b  and  c 
backwards,  closing  the  hole  v  in  d,  and  preventing  the  escape 
of  gas.  The  projectiles  are  shell  and  canister.  In  order  to 
use  shrapnel,  a  heavier  gun  of  3-inch  calibre  has  lately  been 
adopted,  weight  218  Ibs. 

FIELD    GUNS. 

132.  U.  S.  Field  Artillery— 3.6-inch  B.  L.  Mortar— 3.2-inch  B.  L. 

Field  Gun,  Light— 3.6-inch  B.  L.  Field  Gun,  Heavy. 
The  field  artillery  in  the  U.  S.  service  consists  of  the  3.6- 
inch  mortar,  3.2-inch  light  field  gun,  and  3.6-inch  heavy  field 
gun. 

Common  Features.— See  Figs.  102,  103,  and  104.  These 
pieces  are  all  built  of  gun-steel ;  are  breech-loaders,  and  have 
rifled  bores.  They  have  conical  gas-check  seats,  c,  and  cyl- 
indrical powder-chambers,  d,  of  larger  diameter  than  the 
bore,  and  these  chambers  are  connected  with  the  bore  by  a 
conical  slope,  *,  forming  the  seat  for  the  rotating  band  of 
the  projectile,  and  by  which  it  is  centered  in  the  bore. 


GUNS.  235 

In  front  of  this  powder-chamber  slope  is  a  second  conica, 
slope,  /,  which  is  formed  by  cutting  away  the  tops  of  the 
lands  of  the  rifling  to  a  certain  depth  at  the  origin  or  begin- 
ning of  the  rifling,  and  gradually  decreasing  the  depth  of 
this  cut  to  zero,  at  a  certain  distance  from  the  origin,  this 
distance  varying  with  the  size  of  the  piece.  As  a  rule  one 
half  of  the  lands  are  cut  away  at  the  origin.  Thus  for  the 
3.6-inch  gun  the  depth  of  the  rifling  groove  is  0.04  inch, 
and  the  lands  are  cut  away  0.02  inch  at  the  origin.  The  ob- 
ject of  this  rifling  slope  is  to  allow  the  band  of  the  project- 
ile to  enter  gradually  to  its  full  depth  into  the  groove,  and 
thus  diminish  the  strain  due  to  forcing.  It  also  facilitates 
the  loading  of  the  projectiles,  and  tends  to  prevent  the 
escape  of  gas  over  the  band,  as  the  latter  is  forced  readily 
and  quickly  to  the  bottom  of  the  groove. 

3.6-INCH  MORTAR. — This  is  a  short  piece  intended  for 
vertical  fire  against  troops  pro-  _-, 

tected  by  intrenchments  or  irreg- f       1^ 

ularities  of  ground  from  the  direct 
fire  of  the  field  guns. 

It  is  made  of  a  single  piece  of 


steel  (Fig.  102),  and  is  designed  to  FlG-  I02- 

use  the  same  kind  of  powder  and  the  same  projectile  as  the 

3.6-inch  field  gun. 

It  is  mounted  upon  a  cast-steel  carriage,  and  the  weight 
of  piece  and  carriage  are  so  adjusted  that  they  can  be  read- 
ily moved  by  hand. 

3.2  AND  3.6-iNCH  FIELD  GUNS. — The  3.2-inch  gun  (Fig. 
103)  is  intended  for  use  as  a  horse-artillery  gun  for  rapid 
movements,  and  the  3.6-inch  (Fig.  104)  for  the  light  or  field 
battery. 

Common  Features. — The  two  guns  are  exactly  similar  in 
construction,  and  each  consists  of  an  interior  tube,  and  a 
jacket,  assembled  by  shrinkage. 

The  tube  is  inserted  in  the  jacket  from  the  front ;  a 
shoulder,  a,  on  the  tube  resting  against  a  corresponding  one 
on  the  jacket. 

Forward  movement  of  the  tube  in  the  jacket  is  prevented 
by  the  shoulder  b,  as  shown  in  Figs.  103  and  104.  The 


236 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


threads  for  the  breech-block  are  cut  in  the  rear  end  of  the 

jacket,  which  thus  supports  the 
longitudinal  stress. 

The  principal  dimensions, 
etc.,  are  given  in  the  table  page 
253,  with  those  of  the  siege 
guns,  and  of  these,  the  weight 
of  piece,  charge,  and  projectile 
should  be  remembered. 


133.  Breech  Mechanism  of  Field 
Artillery  —  Principal  Parts 
—  The  Breech-block. 

PRINCIPAL  PARTS.  —  The 
breech  mechanism  comprises 
those  parts  which  are  neces- 
sary to  open,  close,  and  lock 
the  breech,  to  prevent  the 
escape  of  gas  in  firing,  and 
through  which  ihe  charge  is 
ignited. 

The  principal  parts  are : 

1.  The  breech-block,  which 
closes  the  breech  and,  by  its 
bearing  on  the  fixed  parts  of 
the  gun,  supports  the  gas-pres- 
sure when  the  charge  is  fired. 

2.  The  obturator,   which 
prevents  the  escape  of  gas. 

3.  The  carrier-ring,  which 
guides  the  block  as  it  is  with- 
drawn from   the  breech,  sup- 
ports  its  weight   when    with- 
drawn,   and    by    which    it    is 
swung  round,  out  of  the  way, 
for  loading. 

4.  The  lever-handle  or  other 
device  by  which  the  block  is 


r 


FIG.  103. 


FIG,   104. 


rotated  after  firing,  and  its  threads  or  bearings  disengaged 
from  those  in  the  breech  of  the  gun. 


GUNS. 


237 


5.  The  vent,  by  which  fire  is  communicated  to  the  charge; 
and  the  vent-closer,  by  which  premature  discharge  is  pre- 
vented. 

THE  BREECH-BLOCK. — In  all  guns  in  the  U.  S.  service, 
except  the  Hotchkiss  mountain-gun  already  described,  the 
breech-block  belongs  to  the  French  or  interrupted-screw 
system.  That  is,  screw-threads  are  cut  around  the  exterior 
cylindrical  surface  of  the  block,  and  around  the  correspond- 
ing interior  cylindrical  surface  of  the  breech-recess.  To 
avoid  the  delay  in  unscrewing  the  block  and  screwing  it 
home  after  and  before  each  discharge,  the  circumferences  of 
the  block  and  breech-recess  are  divided  in  the  field-guns  into 
six  equal  sectors,  and  the  screw-threads  on  every  alternate 


FIG.  105. 

sector  removed,  thus  leaving  on  the  block,  and  in  the  breech- 
recess,  three  threaded  and  three  slotted  sectors  of  equal 
width.  By  this  arrangement  the  block  can  be  pushed  in  or 
pulled  out  of  its  recess,  the  threaded  sectors  on  the  block 
sliding  in  the  slotted  sectors  of  the  breech-recess.  After  it 
is  pushed  home  to  within  one  sixth  of  a  turn  of  the  thread, 
or  one  sixth  of  the  pitch,  a  rotation  through  an  angle  of 
60°  will  cause  the  threads  on  the  block  to  engage  in  those 
in  the  jacket,  and  the  threads  thus  engaged  are  found  to 
have  ample  strength  to  resist  the  pressure  of  the  powder- 
gas.  The  threaded  and  slotted  sectors  of  the  block  are 
partly  shown  in  Fig.  105.  The  exterior  diameter  of  the 
block  at  the  threaded  portion,  is  greater  than  that  of  the 


238  TEXT- BOOK  OF  ORDNANCE   AND    GUNNERY. 

powder-chamber,  in  order  to  give  as  large  a  surface  as  possi- 
ble for  the  screw-threads  and  thus  increase  their  relative 
strength,  and  also  to  leave  a  large  opening  in  the  breech  to 
facilitate  the  insertion  of  the  projectile  and  charge.  The 
length  of  the  block  is  greater  than  its  exterior  diameter,  to 
give  a  greater  number  of  threads,  and  thus  distribute  the 
pressure  of  the  powder-gas  over  a  greater  number  of  them, 
and  reduce  the  stress  on  each,  and  consequently  the  ten- 
dency to  strip.  The  front  face  of  the  block  is  plane,  and  the 
rear  face  has  certain  projections  whose  uses  will  be  explained. 
The  diameter  of  the  unthreaded  portion  in  front  is  less  than 
that  of  the  threaded  portion,  in  order  that  it  may  enter  for 
a  short  distance  into  the  gas-check  seat  in  the  rear  end  of 
the  tube.  The  rear  end  is  not  threaded,  and  has  a  shoulder, 
a,  upon  it,  which  fits  tightly  against  the  rear  face  of  the  car- 
rier-ring when  the  breech  is  closed,  and  thus  prevents  the 
entrance  of  dust  in  transportation.  The  interior  is  bored 
out  for  the  reception  of  the  parts  of  the  obturator,  and  cer- 
tain grooves  are  made  on  the  exterior  whose  object  will  be 
explained. 

134.  The  De  Bange  Obturator — Action — Remarks. 

The  obturator  prevents  the  escape  of  gas  around  the 
threads  of  the  breech-block  and  through  the  mechanism. 
Two  obturators  are  used  in  the  field  service :  the  De  Bange, 
with  the  3.2  and  3.6  rifles,  and  the  Freyre,  with  the  3.6 
mortar. 

THE  DE  BANGE  OBTURATOR.— This  consists  (Fig.  106)  of 
a  central  spindle  or  stem,  a,  terminating  in  front  in  a  large 
head,  b,  called,  from  its  shape,  the  "  mushroom-head  ";  the 
vent,  £,  with  a  copper  bushing,  d,  in  front,  and  the  primer- 
seat,  e,  in  rear ;  two  steel  cups,  //',  called  gas-check  cups, 
and  between  them  a  plastic  pad,  g,  made  of  asbestos  and 
tallow,  strongly  compressed  by  hydraulic  pressure  before 
its  insertion,  and  covered  with  canvas,  the  outer  edges  of 
the  pad  being  protected- by  two  thin  strips  of  copper,  m\  an 
obturator-nut,  h,  held  in  place  by  a  spline-screw,  k,  which  is 
halved  into  the  nut  and  spindle  ;  and  a  spiral  spring,/,  bear- 


GUNS. 


239 


ing  against  a  shoulder  in  the  breech-block,  and  against  the 
front  of  the  obturator-nut,  h. 

When  in  place  in  the  gun,  the  spindle  a  passes  through 
the  axis  of  the  breech-block,  the  outer  surface  of  the  pad  g 


FIG.  1 06. 


rests  against  the  gas-check  seat  in  the  gun,  and  is  held  be- 
tween the  elastic  gas-check  cups//'.  The  mushroom-head 
b  is  in  the  powder-chamber. 

ACTION  OF  THE  DE  BANGE  OBTURATOR. — When  the 
charge  is  fired,  the  gas-pressure  acts  normal  to  the  surface 
of  the  mushroom-head,  and  the  latter,  with  its  spindle  a,  is 
forced  to  the  rear.  The  pressure  is  thus  transmitted  to  the 
gas-check  cups  //',  and  the  elastic  pad  g,  being  held  by 
the  front  of  the  block  and  pressed  between  the  cups  //',  is 
forced  to  expand  radially  and  pressed  firmly  against  the 
walls  of  the  gas-check  seat,  preventing  the  escape  of  gas. 
An  elastic  packing-ring,  n,  also  expands  under  the  pressure, 
and,  fitting  tightly  against  the  spindle  a,  prevents  the  flow 
of  the  tallow  of  the  pad,  and  thus  avoids  the  sticking  of  the 
pad  to  the  spindle.  When  the  pressure  is  removed,  the 
action  of  the  spring  j  keeps  all  the  parts,  cups  and  pad,  in 
place. 

The  pad  has  the  shape  shown  in  order  to  have  as  small 
a  surface  as  possible  in  contact  with  the  spindle  and  the 
wails  of  the  gas-check  seat,  to  avoid  sticking,  and  to  furnish 


240 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


in  the  middle  a  reservoir  of  material  that  may  be  pressed 
outward  and  inward  and  thus  secure  perfect  contact. 

REMARKS.— The  canvas  cover  of  the  pad  prevents  its 
breaking  in  use.  The  shape  of  the  gas-check  cups  is  such 
as  to  avoid  all  sharp  angles  which  would  cut  the  pad,  and 
to  retain  the  edges  of  the  cups  for  preventing  the  flow  of 
the  tallow.  The  elastic  packing-ring  n  also  assists  to  pre- 
vent this  flow.  The  spline-screw  k  prevents  the  unscrewing 
of  the  obturator-nut  h,  which  is  liable  to  occur  when  the 
breech-block  is  rotated  for  withdrawing,  owing  to  the  stick- 
ing of  the  pad  to  the  walls  of  the  gas-check  seat. 

135.  The  Freyre  Obturator — Action — Remarks. 

THE  FREYRE  OBTURATOR. — This  obturator  (Fig.  107)  is 
used  with  the  3.6-inch  mortar,  and  consists  of  a  central  spin- 

XI 


-c 


FIG.  107. 

die,  a,  terminating  in  front  in  a  large  flat  disk ;  the  vent  b  and 
its  copper  bushing,  c,  in  front,  and  the  primer-seat  in  rear ; 
the  threads  and  nuts,  dd' ,  the  rear  nut,  d ',  being  a  locking- 
nut  with  a  left-hand  thread,  while  the  obturator-nut,  d,  has  a 
right-hand  one,  and  hence  df  prevents  d  from  unscrewing 
during  the  rotation  of  the  block ;  the  spiral  spring  et  bear- 
ing on  a  shoulder  on  the  spindle  a  and  a  corresponding 
shoulder  in  the  block,  and  tending  to  push  the  spindle  con- 
stantly forward  ;  and  the  gas-check  ring  /.  The  exterior 
surface,^,  of  the  head  of  the  spindle  is  conical,  and  ground 


GUNS.  241 

to  an  exact  fit  with  the  interior  surface  of  the  conical  gas- 
check  ring,  /.  This  ring  /  is  made  of  steel  of  high  elastic 
limit,  and  when  in  place,  rests  against  the  front  face  of  the 
breech-block  as  shown,  and  its  length  parallel  to  the  axis  of 
the  bore  is  such  that  when  in  this  position  there  is  a  space, 
h,  between  the  head  of  the  spindle  and  the  front  face  of  the 
breech-block.  When  in  place,  the  spindle  a  passes  through 
the  axis  of  the  breech-block,  the  outer  surface  of  the  elastic 
gas-check  ring  /  rests  against  the  walls  of  the  gas-check 
seat,  and  the  front  surface  of  the  spindle-head  is  in  the 
powder-chamber. 

ACTION  OF  THE  FREYRE  OBTURATOR. — When  the  charge 
is  fired,  the  gas,  acting  normal  to  the  spindle-head,  presses  it 
backward  into  the  conical  ring  f,  the  space  h  allowing  this 
movement.  The  ring,  /,  being  held  against  the  face  of  the 
breech-block,  is  thus  forced  to  expand  radially  by  the  wedg- 
ing action  of  the  spindle-head,  and  is  pressed  firmly  against 
the  walls  of  the  gas-check  seat,  preventing  the  escape  of  gas 
around  the  exterior  of  the  ring.  The  tight  fit  of  the  two 
conical  surfaces  prevents  any  escape  between  the  ring  and 
head.  When  the  pressure  of  the  gas  is  removed,  the  elas- 
ticity of  the  ring /and  the  action  of  the  spring  e  return  the 
spindle-head  and  ring  to  their  former  positions. 

REMARKS.  —  This  obturator  has  the  following  advan- 
tages: 

1.  Being  of  metal,  it  is  very  slightly  affected  by  changes 
of  temperature,  weather,  etc. 

2.  It  occupies  very  little  space  in  the  powder-chamber; 
and  hence  when  space  and  consequently  weight  are  impor- 
tant, as  with  this  mortar,  it  is  used. 

Its  disadvantage  is  that  it  is  liable  to  get  out  of  order. 
A  blow  struck  on  the  thin  edge  of  the  ring  f  in  loading,  or 
closing  the  breech,  would  allow  the  gas  to  escape;  and 
after  a  channel  is  once  formed  for  the  gas,  the  obturator 
is  useless.  This  accident  is  liable  to  occur  in  field  service, 
and  to  guard  against  it  to  some  extent  the  spindle-head  is 
made  to  project  well  beyond  the  front  edge  of  the  ring. 
This  projecting  portion  would  ordinarily  receive  any  blow 
which  might  injure  the  edge  of  the  ring/. 


242 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


It  will  be  observed  that  the  spiral  spring  j  in  the  De 
Bange  obturator,  Fig.  106,  acts  in  the  opposite  direction  to 
that  of  the  Freyre,  Fig.  107.  The  reason  is  as  follows:  The 
gas-check  ring  in  the  Freyre  being  elastic,  when  proper 
compression  of  this  ring  is  once  secured  by  the  nuts  ddr,  it 
will  be  retained  unchanged.  With  the  De  Bange  the  pad  is 
not  elastic,  and  hence  il  properly  compressed  before  firing 
this  compression  will  change  after  firing,  due  to  the  great 
pressure  upon  it.  Hence  a  constant  tension  is  always  re- 
quired with  the  De  Bange  to  keep  the  cups  and  pad  in 
place,  while  with  the  Freyre  the  spring  is  used  to  push  the 
spindle  forward,  and  assist  in  restoring  the  ring  to  its  for- 
mer position. 

136.  Carrier-ring — Object  of  Latch. 

CARRIER-RING. — This  ring  guides  the  block,  supports 
its  weight  when  it  is  withdrawn  from  the  breech,  and  en- 
.ables  it  to  be  swung  round  to  one  side  of  the  gun,  out  of  the 
way  of  loading.  It  consists  (Fig.  108)  of  a  ring  of  steel,  h, 


\e 

@ 

/ 

i 
\e 

d' 

£• 

i 

0 

108. 


which  surrounds  the  breech-block,  and  through  which  the 
breech-block  slides  parallel  to  the  axis  of  the  piece.  The 
breech-block  occupies  the  space  a.  On  the  interior  there 
are  three  lugs,  b,  the  exact  width  of  the  slotted  sectors  of 


GUNS.  243 

the  block.  These  lugs  bear  in  the  slotted  sectors,  and  fur- 
nish guides  for  the  block  when  it  is  drawn  to  the  rear,  so 
that  it  is  compelled  to  move  parallel  to  the  axis  of  the  gun. 

On  the  left-hand  side  is  a  stop,  c,  which  travels  in  a 
groove  in  the  breech-block,  and  limits  the  motion  of  transla- 
tion of  the  latter  when  it  is  withdrawn  from  the  breech,  and 
also  its  motion  of  rotation,  when  turned  to  lock  into  the 
threads  of  the  breech  of  the  gun,  or  unlocked  for  withdrawal. 
This  stop  passes  through  the  carrier-ring  and  is  secured  by 
a  screw,  d.  The  stop  may  occupy  any  other  convenient  po- 
sition, and  may  be  a  simple  stud,  as  in  the  case  of  the  mor- 
tar, where  the  stop  is  at  the  top  of  the  carrier-ring. 

Two  lugs,  ee,  are  for  the  purpose  of  attaching  the  carrier- 
ring  to  the  jacket,  by  a  pin  which  passes  through  holes  in 
the  lugs,  and  corresponding  holes  in  the  jacket.  This  pin 
forms  the  axis  around  which  the  carrier-ring,  with  the  block, 
swings,  when  the  breech  is  open  for  loading.  The  exterior 
surface,  g,  of  the  carrier-ring  is  conical,  to  secure  a  good  fit 
in  the  breech. 

OBJECT  OF  LATCH.— When  the  threads  of  the  breech- 
block are  disengaged  from  the  corresponding  threads  in  the 
breech,  the  block  is  pulled  to  the  rear  through  the  carrier- 
ring.  It  is  evident,  however,  that  this  pull  upon  the  block 
will  cause  the  carrier-ring  to  swing  around  the  pin  passing 
through  the  lugs  e,  and  this  will  tend  to  jam  the  block,  and 
prevent  its  movement  to  the  rear.  To  avoid  this,  the  car- 
rier-ring must  be  locked  to  the  gun  while  the  block  is  mov- 
ing to  the  rear.  When  the  travel  of  the  block  is  finished, 
the  carrier-ring  must  be  unlocked  from  the  gun,  in  order 
that  it  may  be  swung  round  with  the  block  to  the  loading 
position.  These  objects  are  accomplished  by  the  latch  /, 
shown  in  Fig.  108  and  in  detail  in  Fig.  109. 

137.  Description  of  Latch  and  its  Working. 

The  latch  consists  of  a  piece  of  metal  shaped  as  shown  in 
Fig.  109.  The  lower  inner  end,  0,  fits  against  one  of  the 
slotted  sectors  of  the  breech-block,  and  is  constantly  pressed 
down  upon  it  by  the  action  of  the  flat  spiral  spring  b,  acting 
on  a  shoulder,  c,  of  the  latch  and  a  corresponding  shoulder, 


244 


TEXT-BOOK  Of   ORDNANCE  AND    GUNNERY. 


d,  of  the  latch-recess. 


a 


b' 


All  the  working  parts  are  covered 
by  the  latch-plate  i  (see  Fig.  108), 
secured  to  the  exterior  of  the 
carrier-ring  by  two  screws,  /,  so 
that  in  case  any  part  breaks  it  may 
be  readily  removed  and  repaired. 
The  front  of  the  carrier-ring  next 
the  breech  has  a  hole,  g,  cut  through 
it,  and  opposite  this  is  a  recess,  k, 
in  the  corresponding  face  of  the 
latch. 

Action   of   the   Latch. — Suppose 
the    breech   closed    and   the    gun 
end    of    the    breech-block   is   a  trans- 


FIG.  109. 

fired.      At  the  rear 

verse  groove,  a,  Fig.  no,  which  is  on  a  level  with  the  slotted 

sector  of  the  block  at  c,  and  gradually  increases  in  depth  to 


.--6 


I 

/JV1VJVTY 

6J 

a 

[e 

d      (e) 

—  ^- 

<*^l 

FIG.    no. 

its  end,  b.  The  depth  of  this  groove  at  b  is  such  that  when 
the  inner  end  of  the  latch  rests  in  it,  the  action  of  the  flat 
spiral  spring,  b,  Fig.  109,  will  force  the  latch  down  sufficiently 
far  to  release  it  from  the  jacket.  The  inner  end  of  the  latch 
rests  at  b  during  firing,  and  hence  at  this  time  the  carrier- 
ring  is  unlocked  from  the  jacket,  and  there  is  no  strain  on 
the  latch.  After  firing,  the  first  operation  in  opening  the 
breech,  is  to  rotate  the  block  in  the  direction  of  the  arrow. 
As  the  latch  is  in  the  carrier-ring,  it  does  not  rotate  with  the 
block,  and  hence  the  action  of  the  groove  a  is  to  push  up 
the  latch  into  its  recess  in  the  breech,  and  thus  lock  the  car- 
rier-ring to  the  jacket.  The  inner  end  of  the  latch  now 
stands  at  c.  The  block  is  now  withdrawn,  the  inner  end  of 


GUNS. 


245 


the  latch  sliding  along  the  slotted  sector,  and  keeping  the 
carrier-ring  locked  to  the  jacket.  This  continues  up  to  the 
point  d. 

At  this  point,  the  path  of  the  inner  end  of  the  latch  be- 
gins to  descend  along  a  gradual  slope  from  d  to  e.  Hence 
by  the  action  of  the  flat  spiral  spring,  the  latch  begins  to 
move  out  of  the  jacket,  being  forced  inward  into  the  groove 
de.  At  the  end  of  the  travel  of  the  block,  corresponding  to 
the  point  e,  the  depth  of  the  groove  de  becomes  sufficient 
to  allow  the  entire  withdrawal  of  the  latch  from  its  recess 
in  the  jacket,  and  hence  at  this  instant  the  carrier-ring 
becomes  unlocked,  and  the  block  and  ring  can  be  swung 
round  for  loading. 

After  Loading. — After  loading,  when  the  block  and  car- 
rier-ring are  swung  round  to  close  the  breech,  the  pressure 
of  the  hand  is  applied  to  the  rear  end  of  the  block.  This 
pressure  would  tend  to  move  the  block  forward  through 
the  carrier-ring,  and  hence  jam  the  ga^-check  against  the 
breech.  The  block  must  therefore  be  locked  positively  to 
the  carrier-ring  in  the  loading  position,  and  this  is  done  as 
follows  : 

The  extremity  e  of  the  groove  a  in  the  block,  termi- 
nates in  a  cylindrical  hole,  into  which  the  inner  end  of  the 
latch  drops  at  the  end  of  its  motion.  The  block  therefore 
cannot  move  with  reference  to  the  carrier-ring,  till  the  latch 
is  lifted  from  this  hole  e.  This  is  accomplished  as  fol- 
lows : 

There  is  a  conical  stud,  s  (see  Fig.  109),  projecting  from 
the  rear  face  of  the  base  ring,  which,  as  the  carrier-ring  is 
closed,  passes  through  the  hole  g,  Fig.  109,  in  the  front  face 
of  the  carrier-ring,  and  enters  the  recess  //  in  the  front  of 
the  latch.  This  stud,  bearing  against  the  inclined  end  of  the 
recess  /*,  owing  to  the  shape  of  the  two  surfaces,  raises  the 
latch  slightly  till  it  clears  the  cylindrical  hole  e,  Fig.  no, 
and  stands  at  such  a  height  that  when  the  block  is  pushed 
forward,  the  lowest  part  of  the  inclined  surface  de  will  pass 
under  the  inner  end  of  the  latch,  and  thus  cause  it  to  move 
up  the  inclined  surface  and  push  the  latch  home. 


246 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


138.  The  Lever-handle. 

This  is  a  device  for  rotating  the  breech-block.  In  the 
mortar  there  are  two  of  these  handles  fixed  to 
the  block  at  opposite  extremities  of  a  diameter 
(Fig.  in). 

In  the  3.2  and  3.6-inch  guns  there  is  one 
handle,  h,  pivoted  to  the  upper  part  of  the 
block  by  a  pin,  e,  Fig.  112.  This  handle  is 
raised  vertically  for  rotation  ;  and  when  low- 
ered for  firing,  its  lower  end  fits  into  a  recess, 
c,  in  the  end  of  the  jacket,  for  additional  secur- 
ity against  accidental  opening.  To  limit  the 
vertical  motion  of  the  handle  when  it  is  raised, 
a  stop,  a,  is  placed  upon  the  pin  e,  which  abuts 
against  a  corresponding  stop,  by  on  the  lug  /. 
The  head  d  of  the  lever-handle,  is  eccentric, 
and  forms  a  cam,  with  the  following  objects: 
When  the  block  is  in  the  firing  position,  this 
cam  d  enters  a  corresponding  recess,  r,  in  the 
rear  face  of  the  carrier-ring,  and  thus  locks  the 
FIG.  i ii^  block  to  the  ring,  and  with  the  end  of  the  lever- 
handle,  as  before  explained,  prevents  any  rota- 
tion of  the  block  in  firing.  When,  after  firing,  the  lever- 
handle  is  raised  and  the  block  rotated,  if  an  attempt  be  made 


FIG.  112. 


GUNS. 


247 


to  withdraw  the  latter,  it  sometimes  fails  on  account  of  the 
sticking  of  the  pad  in  its  seat.  If  the  lever-handle  be  now 
lowered,  the  surface  of  the  cam  d  bears  against  the  rear  face 
of  the  carrier-ring,  since  no  recess  is  cut  for  it  in  this  posi- 
tion, and  thus  exerts  a  powerful  leverage,  sufficient  to  start 
the  pad  from  its  seat. 

The  lever-handle  is  made  to  work  tight  between  its  lugs 
in  the  block,  in  order  that  it  may  not  fly  up  from  its  recess 
in  the  carrier-ring,  by  the  shock  of  discharge. 

In  the  3.2  and  3.6  guns  there  is  a  fixed  bronze  handle,  g, 
attached  to  the  breech-block  for  the  purpose  of  withdraw- 
ing it. 

139.  The  Vent-cover. 

This  is  a  device  to  prevent  the  insertion  of  a  primer,  and 
the  premature  discharge  of  the  piece,  before  the  breech- 
block is  locked.  It  must  be  so  arranged  that  the  vent  will 
be  closed  at  all  times,  except  when  the  threads  of  the  block 
are  engaged  in  those  of  the  breech. 

3.6  Mortar. — For  the  3.6  mortar  the  device  is  as  follows: 
A  handle,  a,  Fig.  113,  is  attached  to  a  shaft,  b,  which  fits 


FIG.  113. 


into  a  recess  on  the  left  side  of  the  breech-block.     The 
shaft  is  shown  in  cross-section  at  c.     When  turned  into  the 


248 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


position  shown  in  the  figure,  so  that  the  vent  is  open,  the 
corner  d  projects  through  the  block,  and  binds  against  the 
edge  of  one  of  the  lugs  /  in  the  carrier-ring,  so  that  when 
in  this  position,  with  the  vent  uncovered,  the  breech-block 
cannot  be  rotated  to  open  the  breech.  The  piece  e  is 
attached  to  the  shaft  b,  and  closes  the  vent.  When  open  or 
closed,  its  ends  rest  on  two  pins,  /,  which  retain  it  in  posi- 
tion, and  its  motion  in  opening  or  closing  is  limited  by  two 
studs,  g.  In  order  to  rotate  the  breech-block,  the  vent  must 
first  be  closed  by  turning  the  shaft  b  upwards  by  the  handle 
a.  The  corner  d  of  the  shaft  then  no  longer  bears  on  the 
edge  of  the  lug  in  the  carrier-ring,  and  the  surface  //  forms 
part  of  the  exterior  curved  surface  of  the  block. 

3.2  and  3.6  Guns. — For  these  guns  a  radial  slot,  a,  Fig.  1 14, 


FIG.  114. 

is  made  in  the  rear  part  of  the  breech-block  which  projects 
outside  the  carrier-ring.  In  this  slot  slides  a  piece  of  metal, 
b,  having  a  pin,  c,  projecting  from  its  forward  face  next  the 
breech  of  the  gun.  A  groove,  d,  is  cut  in  the  rear  face  of 
the  carrier-ring,  which  is  eccentric  at  its  lower  end,  and  the 
pin  c  bears  in  this  groove. 

When  the  block  is  pushed  home,  the  pin  enters  the 
groove  at  e,  and  its  weight  keeps  it  over  the  vent,  as  it 
stands  in  a  vertical  position  during  the  time  the  block  is 
withdrawn.  As  the  block  is  rotated  to  the  right  in  closing, 
the  vent  is  still  covered,  due  to  the  bearing  of  the  pin  c  in 
the  concentric  part  of  the  groove  d.  At  the  last  instant  of 
rotation,  however,  the  pin  c  enters  the  eccentric  part  of  the 
groove  d,  the  vent-closer  is  lifted,  and  the  vent  uncovered. 


GUNS. 


249 


140.  Action  of  Mechanism  of  3.6-inch  Mortar. 

i.  Suppose  the  breech  closed  and  ready  for  firing.  In 
this  position,  the  threads  of  the  block  are  engaged  in  those 
of  the  gun,  the  gas-check  is  in  its  seat,  the  vent-cover  has 
been  moved  to  the  right,  or  downward,  by  hand,  thus  uncov- 
ering the  vent.  By  this  motion  of  the  vent-closer,  the  corner 
of  the  shaft,  as  before  explained,  has  been  caused  to  project 
beyond  the  surface  of  the  block,  and  to  bind  against  the 
edge  of  one  of  the  lugs  of  the  carrier-ring,  so  that  the  block 
cannot  be  rotated  while  the  vent  is  open.  The  inner  end  of 


the  carrier- ring  latch  is  in  the  extremity  d  of  the  transverse 
groove  e,  Fig.  115,  the  outer  end  has  left  its  recess,  g,  in  the 
gun,  and  the  carrier-ring  is  unlocked  from  the  jacket. 

2.  After  firing,  the  elasticity  of  the  spiral  spring  and  of 
the  gas-check  ring  acts  to  move  the  ring  from  its  seat  in  the 
gun,  and  restore  it  to  its  former  position  before  firing. 

The  vent-closer/is  now  turned  upward,  closing  the  vent, 
and  at  the  same  time  unlocking  the  block  from  the  carrier- 
ring,  so  that  it  may  be  turned  to  the  left  by  the  handles  a  a. 
The  block  is  then  turned  to  the  left  60°.  By  this  operation, 
the  threaded  sectors  on  the  block  come  into  the  slotted 
sectors  in  the  breech,  so  that  the  block  can  be  pulled  to  the 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

rear  through  the  carrier- ring.  While  the  rotation  of  the 
block  is  taking  place,  the  inner  end  of  the  carrier-ring  latch 
is  moving  up  the  inclined  groove  <?,  and  the  outer  end  of  the 
latch  has  been  pushed  into  the  recess  g  in  the  jacket,  thus 
locking  the  carrier-ring  to  the  jacket.  The  block  is  now 
pulled  to  the  rear  through  the  carrier-ring  till  its  motion  is 
stopped  by  the  stop  b  in  the  carrier-ring  striking  against  the 
front  shoulder,  b',  of  the  longitudinal  groove  k.  During  this 
motion  of  the  block  the  inner  end  of  the  carrier-ring  latch 
is  bearing  on  the  surface  of  one  of  the  slotted  sectors,  and 
the  carrier-ring  remains  locked  to  the  gun.  Near  the  end  of 
the  motion  of  the  block,  however,  the  inner  end  of  the  latch 
begins  to  descend  along  an  inclined  groove,  /i,  in  the  surface 
of  the  block,  and  the  outer  end,  due  to  the  action  of  the  flat 
spiral  spring  before  described,  is  withdrawn  from  its  recess, 
g,  in  the  gun.  At  the  end  of  the  travel  of  the  block,  this  with- 
drawal of  the  latch  is  complete,  and  the  inner  end  of  the 
latch  drops  into  a  cylindrical  hole,  i,  at  the  end  of  the  inclined 
groove,  thus  locking  the  block  to  the  carrier-ring.  The 
block  and  carrier-ring  are  now  swung  round  by  hand  out  of 
the  way  for  loading. 

3.  To  close  the  breech  the  block  and  carrier-ring  are 
swung  round  into  place.  As  the  carrier-ring  closes  against 
the  breech,  a  conical  stud,  s,  Fig.  109,  on  the  rear  face  of  the 
latter  enters  a  recess  in  the  front  of  the  latch,  and  lifts  the 
inner  end  of  the  latter  out  of  the  cylindrical  hole  i  in  the  block. 
The  block  is  now  pushed  forward  by  hand,  sliding  through 
the  carrier-ring,  the  latch  is  pushed  up  into  its  recess  in  the 
jacket  by  the  action  of  the  inclined  surface  h  on  the  block, 
and  the  forward  motion  of  the  block  is  continued  till  the 
rear  end  of  the  groove  k  strikes  against  the  stop  b.  The 
block  is  then  rotated  to  the  right  60°,  engaging  its  threads 
in  those  of  the  breech.  At  the  same  time  the  inner  end  of 
the  latch  moves  down  the  inclined  transverse  groove  *,  and 
the  upper  end  of  the  latch  is  withdrawn  from  its  recess  g  in 
the  gun,  thus  unlocking  the  carrier-ring  from  the  gun.  The 
rotation  of  the  block  to  the  right  is  limited  by  the  stop  b 
striking  against  the  shoulder  b"  at  the  end  of  the  transverse 
groove  j.  The  vent-closer  is  then  turned  down  by  hand, 


GUNS. 


251 


thus  opening  the  vent  and  locking  the  block  to  the  carrier- 
ring,  and  the  mechanism  is  in  its  firing  posi- 
tion. 

The  action  of  the  mechanism  of  the  3.2  and 
3.6  field-guns  is  exactly  similar,  except  that  the 
vent-closer  is  automatic. 

SIEGE-GUNS. 

141.  5-inch  Gun — 7-inch  Howitzer — 7-inch  Mortar. 
Siege-guns  are  intended  for  attacking  and 
defending  permanent  inland   works,  and  the 
land  fronts  of  sea-coast  fortifications. 
In  the  U.  S.  service  the  pieces  are : 

The  5-inch  siege-gun ; 

The  7-inch  howitzer; 

The  7-inch  mortar. 

Common  Features.  —  These  guns,  like  the 
field-guns,  are  built  of  gun-steel,  and  are  breech- 
loading  with  rifled  bores.  They  have  conical 
gas-check  seats,  and  cylindrical  powder-cham- 
bers of  larger  diameter  than  the  bore,  with 
which  they  are  connected  by  a  conical  slope 
for  centering  the  projectile.  They  have  also 
the  conical  rifling  slope  or  forcing-cone,  formed 
as  explained  in  the  field-guns,  and  for  the  same 
purpose. 

5-iNCH  SIEGE-GUN.— This  gun  is  intended  ^ 
for  direct  fire  in  siege  operations.  It  is  built 
up  (Fig.  116)  of  a  tube,  jacket,  trunnion-hoop, 
a,  sleeve,  b,  locking-ring,  c,  key-ring,  d,  and 
base-ring,  f.  The  tube  is  inserted  into  the 
jacket  from  the  rear.  The  peculiarity  of  this 
gun  is  the  manner  of  assembling  the  trunnion- 
hoop.  It  would  be  preferable  to  have  the 
jacket  and  trunnion-hoop  in  one  piece,  as  in 
the  field-guns,  but  difficulties  in  making  such 
a  forging  of  the  required  physical  qualities 
prevent  this,  and  hence  the  jacket  is  extended 


ll'.'025 


FIG. 


116. 
under  the  trunnion-hoop  to  give  better  support  to  the  tube, 


252 


TEXT-BOOK  OF  ORDNANCE,  AND    GUNNERY. 


and  the  trunnion-hoop  assembled  over  the  front  of  jacket 

as  shown. 

The  surface  of  contact  of  jacket  and  trunnion-hoop  is  a 

cone,  with  the  larger  base  to  the  front,and  this  tends  to  lock 

the  trunnion-hoop  in  place,  and  prevent  any  forward  motion. 
Relative  motion  of  tube  and  jacket  is  prevented  by  the 
shoulder  e  and  base-ring  f.  The  locking-ring 
c  prevents  forward  movement  of  the  sleeve 
b,  which  is  important,  as  the  trunnion-hoop 
abuts  against  b,  and  hence  brings  a  thrust 
upon  it  when  the  piece  is  fired. 

/-INCH  HOWITZER. — This  is  a  compara- 
tively short,  light  piece,  of  large  calibre,  in- 
tended to  carry  a  shell,  with  a  large  bursting 
charge,  and  to  give  a  high-angle  or  curved 
fire,  and  reach  troops  sheltered  by  a  parapet, 
and  also  to  breach  masonry  protected  by 
an  earthen  cover,  to  destroy  earthworks,  etc. 
It  is  built  up  of  a  tube,  a  jacket,  a  trun- 
nion-hoop, a  sleeve,  a  locking-ring,  a  key-ring, 
and  a  base-ring,  assembled  by  shrinkage  (Fig. 
117).  The  construction  is  shown  in  the  fig- 
ure. The  tube  is  inserted  into  the  jacket 
from  the  rear,  and  has  a  shoulder  at  e  which 
prevents  forward  motion.  The  longitudinal 
stress  is  transmitted  from  the  trunnions  to 
the  jacket  through  the  locking-lip  a,  and  for- 
ward motion  of  the  sleeve  b  is  prevented  by 
the  locking-ring  c.  The  key-ring  d  is  shrunk 
over  the  locking-ring. 

7-iNCH  MORTAR. — This  is  a  short  rifled 
piece  intended  to  carry  the  same  shell  as  the 
7-inch  howitzer,  and  give  a  vertical  fire.  It 


FIG.  117. 


is  built  of  a  single  piece  of  forged  gun-steel  (Fig.  118),  and 
resembles  the  3.6-inch  field-mortar. 

Breech  Mechanism. — The  breech  mechanism  of  the  5-inch 
siege-gun  and  7-inch  howitzer,  are  similar  to  that  of  the  3*2- 
inch  gun  already  described.  The  breech  mechanism  of  the 
7-inch  mortar  differs  from  that  of  the  3.6  mortar  in  the  fol- 
lowing particulars  : 


GUNS. 


253 


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254 


TEXT- BOOK  OF  ORDNANCE  AND    GUNNERY. 


FIG.  118. 


1.  It  has  the  De  Bange  gas-check. 

2.  The  vent-closer  is  a  sliding  piece  which  is  moved  over 
the  vent  by  turning  a  handle  similar  to  that  in  the  3.60 

mortar.  This  turning  of  the  handle  to  open 
the  vent  locks  the  breech-block  to  the  carrier- 
ring. 

The  principal  data  relating  to  the  field  and 
siege  artillery  are  given  in  the  table  on  page 
253- 

SEACOAST   GUNS. 

142.  Calibres— Common  Features— 8-inch  Rifle. 

CALIBRES. — The  guns  at  present  adopted 
for  the  U.  S.  seacoast  service  are : 

8-inch  \ 

lo-inch  v  steel  B.  L.  rifles; 

12-inch  ) 

12-inch  steel  B.  L.  mortar; 

12-inch  rifled  mortar,  with  cast-iron  body  and 

steel  hoops. 

COMMON  FEATURES. — The  guns  are  intended  for  direct 
fire  against  armored  ships;  the  mortars,  for  vertical  fire 
against  the  decks  of  war  ships.  The  seacoast  guns,  with  the 
exception  of  the  1 2-inch  mortar  with  cast-iron  body,  are 
built  up  of  gun-steel,  and  are  breech-loading  \vith  rifled 
bores.  They  have  conical  gas-check  seats,  cylindrical  pow- 
der-chambers, which  are  connected  with  the  bore  proper  by 
a  conical  slope,  and  they  have  also  the  rifling  slope,  called 
the  forcing-cone,  already  described  in  the  field  and  siege 
services. 

THE  8-INCH  GUN,  Fig.  119,  is  composed  of  a  tube,  T,  in- 
serted into  the  jacket  from  the  rear,  a  jacket,  J,  two  C  or 
chase  hoops,  one  D  hoop,  four  reinforce  or  A  hoops  (A^ 
being  the  trunnion-hoop),  and  a  base-ring,  R. 

Relative  motion  of  tube  and  jacket  is  prevented  by  the 
shoulder  a  and  the  base-ring.  The  other  shoulders  on  the 
tube  reduce  its  thickness  by  successive  steps  from  rear  to 
muzzle.  C^  and  C^  hoops  are  locked  together  by  a  locking- 
lip,  g,  as  shown,  Fig.  120,  the  smaller  diameter  of  the  lip, 
£T2  being  expanded  sufficiently  by  heat  to  pass  over  the 


G  UNS. 


255 


larger  diameter  of  C\.  This  prevents  relative  motion  of  Cl 
and  Cz  hoops.  The  C  hoops  in  all  guns  have  a  tendency 
to  move  forward,  probably  due  to  the  vibration 
T  of  the  chase  and  other  causes,  and  to  prevent  this, 
four  pins,  /,  Fig.  121,  pass  through  the  C^  hoop 
radially  into  the  tube.  The  D  hoop  overlaps  the 
joint  between  jacket  and  Cl  and  by  means  of  the 
shoulders  at  c  and  c',  locks  the  6\  hoop  to  the 
jacket,  and  hence  the  jacket  and  £\  are  not  locked 
together  by  a  lip.  The  small  ring  e  is  called  a 
filling-ring.  It  is  necessary,  because  in  assembling 
the  D  hoop  it  is  desirable  to  make  a  tight  contact 
at  the  shoulders  c  and  c' .  The  rear  end  of  D  is 
therefore  made  of  such  length  as  when  hot  to  fill 
the  space  from  c  to  jacket-shoulder.  Hence  when 
cold  there  will  be  an  opening  at  b,  which  is  filled 


FIG.  120. 


FIG.  121. 


by  turning  out  a  groove,  and  driving  into  it  a  split 
ring  of  metal,  e.  This  gives  stiffness  to  the  chase. 
The  trunnion  or  At  hoop  abuts  against  a  shoulder 
on  the  jacket  at  d.  The  longitudinal  strain  due  to 
firing  is  then  distributed  along  the  jacket  from 
the  base-ring  to  the  shoulder  d. 

The  reinforce  or  A  hoops  are  not  locked,  be- 
cause there  is  no  tendency  to  slide  in  these  hoops, 
and  the  reinforce  does  not  require  stiffening. 

As  a  rule,  it  may  be  observed  that  the  locking 
of  hoops  together  is  for  two  purposes  : 

1.  To  obtain  longitudinal  stiffness. 

2.  To  prevent  sliding. 

Hence  reinforce-hoops  need  no  locking,  and 
chase-hoops  are  not  locked  when  the  joint  be- 


FIG.  119. 
tween  them  is  overlapped  by  an  exterior  hoop. 


256 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


143.  The  10  and  12-inch  Rifles. 

In  these  guns  (Fig.    122)  the  tube  is  inserted  into  the 
jacket  from  the  front,  as  in  the  field-guns,  and  the  breech- 
_    screw  threads  are  cut  in  the  jacket. 

The  parts  of  the  10  and  1 2-inch  guns  are  : 

One  tube ; 
One  jacket ; 
Two  C  hoops ; 
One  D  hoop  ; 
Three  A  hoops ; 
Three  B  hoops  ; 
Four  securing-pins,  f\ 
One  filling-ring,  e. 

The  following  features  of  construction  may 
be  noted :  There  are  relatively  few  pieces,  and 
consequently  the  hoops  are  very  long.  This 
gives  great  longitudinal  stiffness.  The  chase- 
hoops  are  locked  together  by  a  locking-lip,  g, 
and  the  sliding  of  these  hoops  prevented  by  the 
four  pins/. 

In  the  10  and  12-inch  guns  there  is  no  shoul- 
der in  the  jacket  to  prevent  forward  motion  of 
the  tube.  This  motion  is  therefore  prevented 
by  the  bearing  of  the  C^  hoop  against  the  shoul- 
der a  on  the  tube,  and  the  Cl  hoop  is  held  in 
place  by  the  D  hoop  locking  over  two  shoul- 
ders, one  on  the  jacket  at  c',  and  the  other  on 
the  Cl  hoop  at  c. 

The  D  hoop  is  shrunk  on  over  these  shoul- 
ders as  shown  in  the  figure,  locking  the  jacket 
and  (7,  hoop  together ;  and  as  tight  joints  must 
be  made  at  c  and  c',  the  length  of  the  D  hoop 
must  be  such  as  to  exactly  fill  the  space  between 
b  and  the  shoulder  on  the  jacket  at  c'  when  hot. 
Hence  when  cold  it  will  leave  an  open  joint  at 
'7,  and  this  is  filled  by  turning  out  a  groove  and 
putting  in  the  filling-ring  e.  It  will  be  observed 
FIG.  122.  that  this  same  construction  is  used  in  the  8-inch 


GUNS. 


257 


FIG.  126. 


FIG.  123.  FIG.  124.  FIG.  125.  FIG.  127. 


258 


TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 


gun;  but  it  is  of  greater  importance  here,  as  the  Cl  hoop  is 
depended  on  to  hold  the  tube  in  place,  while  in  the  8-inch 

gun  a  shoulder  on  the  jacket  does 
this.  The  A3  hoop  has  a  shoulder, 
m,  near  its  rear  end  which  fits  over 
a  corresponding  shoulder  on  the 
jacket.  By  the  shrinkage  of  the  A3 
hoop  on  the  jacket  it  has  a  firm  hold 
on  the  latter,  and  hence  this  shoul- 
der on  the  jacket,  bearing  against 
the  shoulder  on  A3,  strengthens  the 
jacket  longitudinally,  since  it  dis- 
tributes a  portion  of  the  pull  of  the 
breech-block  to  the  Aa  hoop.  The 
forward  thrust  of  the  trunnion-hoop 
Bl  is  transmitted  to  the  shoulder  n 
on  the  Al  hoop,  and  from  the  Al 
hoop  to  the  jacket  by  the  shoulder  d. 
Thus  the  jacket  takes  the  longitudi- 
nal strain  in  all  cases.  Figs.  123  to 
127  show  the  8,  10,  and  1 2-inch  guns 
drawn  to  the  same  scale  and  giving 
their  relative  sizes,  and  also  the  12- 
inch  mortars,  which  are  to  be  de- 
scribed. 


144.  12-inch  Steel  Mortar — 12-inch  Cast- 
iron  Mortar,  Steel-cooped. 
12-iNCH  STEEL  MORTAR.  —  This 
mortar,  Fig.  128,  is  composed  of — 

One  tube ; 
One  jacket; 
Two  C  hoops ; 
One  D  hoop  ; 
Three  A  hoops  ; 
One  base-ring. 

The   tube   is    inserted    into   the 
jacket  from  the  rear,  as  in  the  8-inch 

As  the 


FIG.  128. 


FIG.  129. 
gun,  and  the  shoulder  a  prevents  motion  of  tube. 


GUNS.  259 

piece  is  short,  and  therefore  stiff,  the  C  hoops  are  not  locked, 
but  four  radial  securing-pins  are  inserted  in  the  muzzle-hoop 
to  prevent  sliding. 

12-iNCH  MORTAR  WITH  CAST-IRON  BODY,  STEEL-HOOPED. 
— This  mortar,  Fig.  129,  was  designed  before  the  1 2-inch 
steel  mortar,  with  the  object  of  procuring  a  high-power 
B.  L.  mortar  which  would  be  cheap  and  could  be  made  in 
large  quantities.  The  value  of  mortar-fire  depends  on  group- 
ing a  large  number  of  mortars  in  one  place  and  under  the 
control  of  one  person,  who  can  thus  drop  a  number  of  pro- 
jectiles in  a  given  area,  and  compensate  by  the  number  of 
shots  for  the  lack  of  accuracy.  Hence  the  necessity  for 
cheapness.  It  is  found,  however,  that  the  steel  mortar  has 
greater  power  and  endurance,  and  it  is  possible  that  the 
manufacture  of  cast-iron  mortars  will  be  abandoned. 

The  mortar  consists  of — 

The  cast-iron  body ; 
Five  A  hoops ; 
Six  B  hoops. 

The  only  point  in  the  construction  that  requires  notice 
is  that  the  Ab  hoop  is  shrunk  on  the  cast-iron  body  over  two 
shoulders,  ad.  This  is  for  the  purpose  of  strengthening  the 
cast  iron  longitudinally  against  the  pull  of  the  breech-block, 
and  is  similar  to  the  method  adopted  in  the  10  and  12-inch 


145.  Breech  Mechanism — Block — Obturator — Anti-friction  Washers 
and  Spring. 

The  breech  mechanisms  of  the  8,  10,  and  12-inch  guns 
are  essentially  the  same.  That  for  the  mortar  differs  in 
some  respects  from  the  guns. 

The  essential  parts  of  the  mechanism  are : 

The  breech-block ; 
The  obturator ; 
The  console  or  tray  ; 

The  device  for  rotating  and  withdrawing  the  breech- 
block ; 
The  vent  and  vent-closer. 


26o 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


BREECH-BLOCK. — This  resembles  the  blocks  already  de- 
scribed for  the  field  and  siege  artillery.  In  the  8-inch  gun 
there  are  three  threaded  and  three  slotted  sectors  ;  in  the 
10  and  12-inch,  four. 

The  rear  end  of  the  block  is  left  unthreaded  for  some 


TUBE. 


i 


*•> — FULL  SIZE.- 


FIG.  130. 

distance,  ab,  Fig.  130.     The  cylinder  of  metal  thus  formed, 

fits  accurately  into  the  breech-recess,  when    the  block    is 

home,  and  prevents  the  entrance  of  sand  or  dust,   which 

might  cause  jamming  of  the  threads. 

OBTURATOR. — This  is  the  De  Bange  system  modified, 

and  differs  from  that  used  in  the  field  and  siege  services  as 

follows  (Fig.  130) : 

The  front  cup  is  replaced  by  a  split  steel  ring,*:,  shown  in 

detail  in  Fig.  131,  fitted  against 
the  outer  portion  of  the  mush- 
room-head. The  rear  gas-check 
cup  is  replaced  by  a  flat  disk  of 
steel,  d,  fitting  tightly  against 
the  front  of  the  block.  A  split 
steel  ring,  ^,  similar  to  <:,  takes 
the  place  of  part  of  the  outer 
edge  of  the  gas-check  cup  for- 
merly used,  and  another  split 
ring,/,  fits  against  the  spindle. 

When  the  gas-pressure  acts,  these  rings  expand,  and  pre- 


FIG.  131. 


GUNS.  26l 

vent  the  flame  and  gas  from  reaching  the  covering  of  the 
gas-check  pad,  and  also  from  penetrating  in  the  direction  of 
the  spindle.  When  the  pressure  is  relieved  the  rings  resume 
their  normal  size,  and  tend  to  cause  the  pad  to  leave  its  seat 
in  the  gun,  and  thus  prevent  sticking. 

ANTI- FRICTION  WASHERS  AND  SPRING. — In  all  guns 
using  the  De  Bange  fermeture,  the  pad  is  liable  to  stick  in 
its  seat  after  firing,  and  render  the  breech  difficult  to  open. 
This  is  provided  for  in  the  field  and  siege  guns  by  the  cam 
-action  of  the  head  oi  the  lever-handle,  as  has  been  ex- 
plained. 

In  the  sea-coast  service,  the  lever-handle  is  not  used  for 
rotating  the  block,  as  it  is  not  sufficiently  powerful,  and  the 
following  arrangement  is  adopted  to  overcome  the  sticking 
of  the  pad : 

By  referring  to  the  field-gun  mechanism,  it  will  be  seen 
that  there  is  a  spring,/,  between  the  obturator-nut  h,  Fig.  106, 
and  the  shoulder  in  the  block.  Hence  when  the  block  is 
rotated,  it  moves  back  ^  of  the  pitch  of  its  thread,  compress- 
ing this  spring  and  allowing  the  pad  to  remain  fast  in  its  seat. 
At  the  end  of  the  rotation  the  cam  action  of  the  lever-handle 
draws  out  the  pad  from  its  seat. 

In  the  large  guns,  the  spring  is  replaced  by  two  anti- 
friction washers  of  steel,  g,  and  two  of  brass,  h,  of  the  shape 
shown  in  Fig.  130.  Each  alternate  washer  is  of  brass,  so  that 
two  metals  of  the  same  kind  shall  not  rub  against  each  other. 
A  cup-shaped  spring  i  jests  against  a  shoulder  on  the  front 
€nd  of  the  obturator-nut  /,  and  bears  on  the  shoulder  of  the 
block.  This  spring  acts  as  a  cover  to  keep  out  dust.  The 
action  is  as  follows  : 

When  the  block  is  rotated,  it  moves  back  \  or  -J  of  the 
pitch  of  its  thread.  This  brings  a  pressure  upon  the 
washers,  which  is  thence  transmitted  to  the  obturator-nut, 
and  by  this  pressure  the  pad  is  loosened  in  its  seat.  The 
object  of  the  anti-friction  washers  is  to  allow  this  rotation 
of  the  block  to  occur  independently  of  the  spindle,  and  this 
is  done  by  diminishing  the  lever-arm  of  the  friction. 

rs  -  r'3 
The  value  of  this  arm  is,  from  mechanics,  — 7^-,  in 


262 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


which  r  and  r'  are  the  exterior  and  interior  radii  of  a  ring. 
By  giving  a  double-convex  section  to  the  washers,  r  is  de- 
creased and  r'  increased  ;  and  hence  the  moment  of  the  fric- 
tion with  reference  to  the  axis  of  the  spindle  is  sufficiently 
decreased  to  allow  the  spindle  to  stand  fast  while  the  block 
rotates. 

146.  Apparatus  for    Rotating  and  Withdrawing  the  Breech-block 

— The  Tray — The  Translating  Screw. 

ROTATING  DEVICE. — The  lever-handle  cannot  be  used 
for  rotating  the  breech-block  in  sea-coast  guns  owing  to  its 


FIG.  132. 

lack  of  power.     The  device  adopted  is  called  the  "  rotating- 
ring,"  and  is  shown  in  Fig.  132. 

It  is  a  ring  of  steel  encircling  the  breech-block,  and  hav- 
ing a  lug,  a,  the  exact  width  of  one  of  the  slotted  sectors, 
projecting  on  the  interior.  This  lug  enters  one  of  the 
slotted  sectors  of  the  block,  and  the  remainder  of  the  in- 
terior circle  is  of  such  diameter  that  the  breech  block  will 
slide  through  it.  On  the  exterior  there  is  a  projecting 
toothed  sector,  b,  which  gears  into  a  pinion,  p.  When  the 
pinion  is  rotated  by  a  crank,  £,  motion  is  communicated 


G  UNS. 


26j 


to  the  rotating-ring,  and  through  the  lug  a  to  the  block. 
The  rotating-ring  is  held  in  place  against  the  rear  face  of 
the  breech,  by  a  steel  plate,  called  the  "  breech-plate," 
which  allows  rotation,  but  prevents  any  other  motion.  The 
rotation  of  the  ring  and  block  is  limited  to  an  angle  of 
60°  or  45°,  according  to  the  gun,  by  the  surfaces  c  c'  strik- 
ing against  corresponding  surfaces  in  the  breech-plate.  The 
rotation  of  the  block  having  been  completed,  it  can  be 


REAR  END   VIEW. 
FIG.  133. 

withdrawn  from  the  breech,  sliding  through  the  rotating- 
ring. 

THE  TRAY  OR  CONSOLE. — In  the  field  and  siege  guns, 
the  block,  when  withdrawn,  is  supported  by  a  carrier-ring. 
In  the  sea-coast  guns,  this  method  will  not  answer,  as  the 
carrier-ring  does  not  furnish  sufficient  bearing-surface  to 
support  the  block.  A  tray  is  therefore  used  for  this  pur- 
pose, and  is  shown  in  Fig.  133. 

It  is  made  of  brass,  and  is  hinged  to  the  rear  face  of  the 
breech,  by  a  steel  pin  passing  through  the  hub  b. 


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TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


The  tray  swings  around  this  pin,  and  with  the  block  may 
be  rotated  to  the  right,  out  of  the  way  for  loading. 

TRANSLATING-SCREW. — Near  the  middle  of  the  tray  is  a 

hole,  c,  which  is  threaded,  and  a 
slot  cr  is  cut  in  its  top,  parallel  to 
the  axis  of  the  hole.    In  this  hole 
FlG-  I34>  c,  works  a  double-threaded  screw 

called  the  translating-screw,  Fig.  134,  the  threads  being 
right  and  left  handed,  and  one  of  them 
narrower  and  more  shallow  than  the 
other.  The  shallow  thread  engages 
in  the  corresponding  thread  in  the 
hole  c,  Fig.  133,  so  that  the  screw 
when  turned,  will  move  in  or  out  of 
the  tray.  On  the  rear  end  of  the 
breech  -  block  there  is  a  projecting 
stud,  b,  Fig.  135,  called  the  translating- 
stud.  When  the  breech  -  block  has 
rotated  one  sixth  of  a  turn  to  the  left,  this  stud  moves 
down,  and  engages  in  the  larger  thread  of  the  translating- 
screw.  Hence  when  this  screw  is  rotated,  it  withdraws  the 
block  from  its  recess  with  a  motion  equal  to  the  sum  of  the 
pitches  of  the  two  threads,  for  each  revolution  of  the  screw. 

147.  Remaining  Parts  of  Breech  Mechanism — Guide-rails — Guide- 
grooves— Side-latch— Tray  Latch. 

On  each  side  of  the  tray  (Fig.  133)  are  two  projections, 
aa' ,  equidistant  from  the  screw.  They  are  called  the 
"  guide-rails." 

On  the  under  side  of  the  breech-block,  at  equal  distances 
from  the  translating-stud,  are  two  grooves,  aa',  Fig.  135, 
called  "  guide-grooves."  These  grooves  do  not  extend  the 
whole  length  of  the  block,  but  end  abruptly  at  shoulders. 
When  the  block  is  withdrawn  by  the  translating-screw,  the 
guide-grooves  slide  on  the  guide-rails,  which  thus  furnish  the 
bearing  for  the  block,  and  the  block  continues  its  movement 
to  the  rear  till  it  is  suddenly  stopped  by  the  striking  of  the 
shoulders  of  the  grooves  aa'  on  the  front  ends  of  the  guide- 
rails  of  the  tray. 


GUNS.  265 

During  this  motion  of  the  block  the  translating-stud  b, 
Fig.  1 35,.  travels  in  the  slot  cr,  Fig.  133,  being  always  engaged 
in  the  larger  thread  of  the  translating-screw. 

SIDE  LATCH. —  When  the  block  has  reached  the  end  of 
its  travel,  the  tray  and  block  are  swung  by  hand  to  the  right 
for  loading. 

To  hold  the  tray  and  block  in  this  position,  and  prevent 
the  accidental  closing  of  the  breech,  by  the  swinging  in  of 
the  tray,  a  catch  is  provided  on  the  under  side  of  the  tray, 
and  a  side  latch  on  the  breech  of  the  gun.  This  latch  catches 
the  tray  as  it  swings  around,  and  retains  tray  and  block  till 
the  latch  is  lifted  by  hand. 

TRAY -LATCH.  —  When  the  tray  and  block  are  swung 
around  after  loading,  into  the  position  for  the  insertion  of 
the  block  in  the  breech,  the  block  is  moved  forward  along 
the  tray  by  the  translating-screw. 

But  in  order  that  the  block  may  enter  its  recess  in  the 
breech,  the  tray  must  fit  accurately  against  the  rear  face  of 
the  breech,  so  that  the  guide-rails  shall  be  parallel  to  the 
axis  of  the  bore. 

Again,  as  soon  as  the  block  enters  its  recess  and  begins 
to  bear  on  it,  the  thrust  of  the  translating-screw  will  tend  to 
move  the  tray  back  from  the  breech.  There  must  be  some 
arrangement,  therefore,  to  latch  the  tray  against  the  breech, 
and  hold  it  in  that  position  till  the  block  is  home,  and  this  is 
the  object  of  the  tray-latch.  This  latch  fits  into  a  recess,  d, 
Fig.  133,  in  the  lower  part  of  the  tray,  and  engages  in  a  cor- 
responding recess  in  the  breech  of  the  gun.  It  is  shown  in  Fig. 
136.  It  is  constantly  acted  on  by  the  spring-lock^  which  keeps 
it  engaged  in  the  recess  in  the 
breech  of  the  gun.  The  upper 
end  of  this  lock  bears  against 
the  translating-screw  in  the 
tray,  and  hence  the  lock  can 

rise  and  the  tray  be  unlatched 

FIG.  136. 
only    when    the    end     of   the 

translating-screw  is  beyond  the  lock  c.  This  happens  When 
the  block  is  withdrawn.  The  sudden  shock  of  the  block 
striking  against  the  guide-rails  in  its  outward  motion,  is 


266 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


FIG.   137. 


communicated  to  the  latch,  and  acting  obliquely,  a  force 
perpendicular  to  the  axis  of  the  latch  is  developed,  of 
sufficient  intensity  to  disengage  it  automatically  from  the 
breech. 

148.  Vent-cover— Action  of  Breech  Mechanism. 

VENT-COVER. — This  consists  of  a  flat  piece  of  steel,  a, 
Fig.  137,  pivoted  loosely  in  the  breech-block. 

The  head  of  this  piece  bears  against  the  inner  surface  of 
the  breech-recess  as  the  block  rotates, 
and  hence  it  cannot  move  around  the 
pivot,  but  remains  in  the  same  radial 
position  covering   the  vent.     At  the 
end  of  the  rotation  of  the  block,  when 
the  threads  are  engaged  in  those  of 
the  breech-recess,  the  head  drops  into 
a   groove   cut   for    it   in   the   breech 
recess,  and   the  vent-closer    assumes 
the  position  a',  uncovering  the  vent. 
When  the  block  is  rotated  to  the  left  for  unlocking,  the  first 
motion  brings  the  head  to  its  bearing  against  the  breech-re- 
cess, and  thus  closes  the  vent. 

ACTION  OF  BREECH  MECHANISM — Breech  Closed. — In  this 
position  of  the  block  its  threads  are  engaged  in  those  of 
the  breech-recess,  the  gas-check  is  in  its  seat  in  the  tube, 
the  vent-cover  has  moved  to  the  right,  uncovering  the 
vent,  the  tray  is  latched  to  the  breech  by  the  tray-latch, 
and  the  translating-screw  is  in  its  recess  as  far  as  it  will 
enter. 

To  Open  the  Breech. — Turn  the  crank  attached  to  the  pin- 
ion of  the  rotating-ring,  in  the  direction  indicated  by  the 
arrow  on  the  breech.  This  motion  is  communicated  to  the 
rotating-ring  through  the  toothed  sector,  and  from  this 
ring  to  the  breech-block,  by  the  lug  which  enters  its  slotted 
sector.  As  the  block  begins  to  rotate  to  the  left,  the  vent- 
closer  closes  the  vent  as  explained.  When  the  block  has 
rotated  one  sixth  of  a  turn,  the  translating-stud  enters  the 
thread  of  the  translating-screw  in  the  tray.  This  screw  is 
then  rotated  by  its  crank,  and  the  block  withdrawn  from  its 


GUNS. 


267 


recess  in  the  breech.  At  the  end  of  its  travel  tne  shoulders 
on  the  block  strike  against  the  ends  of  the  guide-rails  on 
the  tray,  and  the  shock  disengages  the  tray-latch  from  the 


FIG.  138. 

breech.     The  tray  and  block  can  now  be  swung  around  for 
loading. 

To  Close  the  Breech.— Lift  the  side  latch;  swing  the  tray 
and  block  around  to  the  left  till  the  tray-latch  is  engaged 


268 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


in  its  recess  in  the  breech.  The  block  is  now  driven  home 
by  the  translating-screw. 

Rotate  the  block  to  the  right  by  the  rotating-crank,  and 
when  the  rotation  is  finished,  the  block  will  be  in  the  posi- 
tion first  described  and  the  gun  ready  for  firing. 

The  mechanism  for  the  10  and  12  inch  guns  is  so  similar 
to  this  that  no  special  description  is  necessary. 

149.  Breech  Mechanism  of  12-inch  Mortar. 

In  this  piece  the  mechanism  differs  from  that  of  the  guns 
as  follows: 

Rotating  Device. — On  the  rear  face  of  the  breech-block  is 
fixed  a  steel  plate,  k,  Fig.  139,  called  a  face-plate.  The  upper 


FIG.  139. 

end  or  stem  of  this  face-plate  is  cut  out,  and  carries  two  gears, 
a,  b,  and  on  the  exterior  a  third  gear,  c,  on  the  same  shaft 
with  b.  Motion  is  communicated  to  these  gears  by  the 
crank  d.  On  the  rear  face  of  the  breech  is  a  circular  rack  e, 
with  which  the  gear  c  engages,  when  the  block  is  pushed 
home.  It  is  evident  that  a  rotation  of  the  crank  d  will  cause 
the  face-plate  and  block  to  rotate  to  the  right,  or  a  reverse 
motion  of  the  crank,  when  the  breech  is  closed,  will  cause  a 
rotation  of  the  block  to  the  left.  The  block  is  withdrawn 


GUNS.  269 

by  a  translating-screw  as  before.  The  tray-latch  is  the  same 
in  principle  as  in  the  guns,  the  only  change  in  construction 
being  that  the  spring-lock  acts  in  front  of  the  pivot,  and  the 
latch  rises  when  it  is  disengaged. 

Vent-closer. — This  resembles  that  used  in  the  3.2-inch 
gun,  and  consists  of  a  piece  of  metal,/,  sliding  in  a  slot  in 
the  face-plate.  A  pin  projecting  from  the  front  of  this  slid- 
ing-piece,  bears  in  a  groove  g  in  the  rear  face  of  the  breech, 
which  is  concentric  for  some  distance  with  the  axis  of  the 
breech-block,  and  at  its  lower  extremity  becomes  eccentric. 
Its  action  in  uncovering  the  vent  is  the  same  as  in  the  case 
of  the  3. 2-inch  guns. 

Action  of  Mechanism. — When  the  block  is  closed,  the  head 
of  the  face-plate  is  at  the  right-hand  end  of  the  rack  e,  the 
crank  d  is  parallel  to  the  axis  of  the  face-plate,  and  is  held 
in  place  by  a  spring-lock  h.  After  firing,  the  crank  d  is 
turned,  and  the  gear  c  engaging  in  the  rack  e,  rotates  the 
block  to  the  left. 

The  rotation  of  the  block  is  limited,  by  the  striking  of  the 
sides  of  the  face-plate  against  the  ends  of  the  circular  recess 
in  which  the  rack  is  placed.  The  block  is  now  withdrawn 
by  the  translating-screw,  and  block  and  tray  swung  round 
for  loading. 

To  close  the  breech  the  operations  are  reversed. 

150.  Improved  Mechanism — Continuous  Rotation. 

Objections  to  Ordinary  Mechanism.  —  In  the  mechanism 
already  described,  one  crank  is  necessary  to  rotate  the 
block,  and  at  the  end  of  this  movement,  the  power  must  be 
transferred  to  another  crank  for  withdrawing  the  block. 
When  the  block  is  withdrawn,  the  power  must  be  applied 
to  the  handle  of  the  tray  to  swing  the  block  and  tray 
around.  We  have  thus  three  separate  and  djstinct  mo- 
tions, involving  loss  of  time,  and  complication  of  mechan- 
ism. 

IMPROVEMENTS. — In  the  latest  improved  mechanism,  the 
object  is  to  effect  by  the  application  of  power  to  one  crank, 
and  by  its  continuous  movement,  the  rotation,  translation, 
and  swing,  of  the  block  and  tray. 


2/O 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


This  mechanism,  as  applied  in  our  service,  is  called  the 
Farcot,  from  its  inventor,  and  consists  (Fig.  140)  of  the  fol- 
lowing parts : 

On  the  right  side  of  the  rear  end  of  the  breech-block  is 
a  circular-toothed  sector  a.  A  cut  is  made  in  one  of  the 
threaded  sectors  of  the  block  parallel  to  its  axis,  and  this 
circular  rack  is  extended  along  the  block  as  shown  in  the 
figure  (plan),  the  width  of  this  longitudinal  rack  b  being 
that  of  the  thickness  of  the  wheel  c,  while  the  width  of 


FIG.  140. 


the  circular  sector  a  is  one  sixth  of  the  circumference  of 
the  block.  On  the  top  of  the  hinge-pin  d,  is  mounted  a 
worm-gear  c,  whose  teeth  fit  the  corresponding  teeth  of  the 
sector  a. 

At  the  bottom  of  the  hinge-pin  d  is  a  second  worm- 
gear,  e.  A*  horizontal  crank-shaft,  /,  has  at  the  right  end  a 
worm,  g,  gearing  into  the  worm-gear  e,  and  at  the  left  end  a 
crank,  h. 

Action  of  Mechanism.  —  When  the  crank  h  is  turned, 
motion  is  communicated  to  the  worm-gear  c  through  g  and 
e,  and  the  action  of  c  on  the  sector  a  rotates  the  block  one 


GUNS. 


2/1 


sixth  of    a  turn,   till  the   shoulders  kl  on  the   block  strike 
against  the  guide-rails  mn. 

The  block  then  being  no  longer  able  to  turn,  the  teeth  of 
the  wheel  c,  engaging  in  those  of  the  rack  by  along  the  block, 
will  force  the  block  to  the  rear  out  of  the  breech-recess. 
The  cut  in  the  threaded  sector  of  the  block,  for  the  reception 
of  the  rack  b,  is  made  so  deep  that  the  worm-wheel  c  binds 
against  the  edges  of  this  cut  in  travelling  along  the  rack, 


TABLE  II. — BREECH-LOADING  ORDNANCE,  U.  S.  LAND  SERVICE. 


Seacoast  Guns,  Steel.                        jSeacoast  Mortars. 

Model        Model 
1888,  M.    1888,   M. 

Model 
1888,   M. 

Model 
1892. 

Pro- 
posed. 

Cast  iron 
Steel  - 
hooped. 

Steel. 

Calibre    inches  

8 
J  32,372  I 
1  32-480  f 
M-S 
23.21 
32 

30 
9-5 
i.  08 
3 
51,980 

48 
0.3736 
0.06 

j  t  in  50  to 
j    i  in  25 

i4,!25 

3,597 
5°  -75 
25.66 

GO 
i«S 

0.9619 

300 

i  to  108 

37,000 
J,95° 
7,9°7 

16.0 
10.6 

10 

67,200 

3° 
30.60 

34 
38.5 
ii.  8 

«.*3 

4 
53.09o 

60 
0.3736 
0.06 
0.15 
i  in  50  to 
i  in  25 

28,977 
7,064 
65.09 
27-51 

c« 

250 
0.9797 

575 
i  to  117 

37,000 
1-975 
15-548 

20.4 
14.6 

12 

116,480 

52 
36.66 

34 
46.2 
14.2 
1,125 
4 
53,000 

72 
0.3736 
0.06 
0.15 
i  in  50  to 
i  in  25 

50,049 
12,092 

77-33 
27.58 

to 

450 
i  .0285 

1,000 

i  to  116 

37,000 
i,975 
27,040 

24.9 
18.7 

12 
128,719 

57-5 
40.0 

37-83 

46.4 
14-5 

1.  10 

4 

52,640 

72.0 
o-3736 
0.06 
0.15 
i  in  50  to 
i  in  25 

55,829 
12,798 
78.58 
31.29 

(d) 
487 
1-0535 

1,000 

16 
280,000 

**5 

49.67 

35 
62 
18.8 
1.148 
4 
53,000 

96 
0.3736 
0.07 
0.15 
i  in  50  to 
i  in  25 

121,487 
29,34i 
106.06 
28.37 

(d) 

i,  060 

i 

2,370 

12 
31,920 
14.25 
10-75 

9 
4I-75 
12.4 
1.18 
3 
29,490 

68 
c  379 
0.07 

0.175 

i  in  40  to 
i  in  25 

12,554 
1,990 
iS-75 
7.66 

00 

80 

1.1128 

j     800 

|      1,000 

12 
29,120 

11 
II.76 
10 

38 
12.5 
1.02 

3 
50,200 

72 
0-3736 
0.06 
0.15 
i  in  40  to 
i  in  20 

J3>947 
2,636 

20.8 

8.225 

CO 

105 

I  .  1026 

800 

1,000 

I  to  36 

30,000 
1,140 
7,207 

9-7 

Weight: 
Pounds      

Tons 

Total  length,  feet  
Length  of  bore,  calibres..  .  . 
Diameter     over     powder- 
chamber,  inches  
Diameter  of  powder-cham- 
ber, inches  
Thickness     over     powder- 
chamber,  calibres  
Number  of  cylinders  com- 
prised in  the  thickness.  . 
Maximum  tangential  resist- 
ance, pounds  per  sq.  in.  . 
Rifling: 
Number  of  grooves  
Width  of  grooves,  inches 
Depth  of  grooves,  inches 
Width  of  lands,  inches... 

Twist,  calibres  

Total    capacity     of     bore, 
cubic  inches.    .  .    
Capacity  of  powder-cham- 
ber, cubic  inches   .  .  
Lengthof  powder-chamber, 
inches  

Travel  of  projectile  in  bore, 
calibres  
Powder  charge: 
Kind 

Weight,  pounds  
Density  of  loading 

Projectile: 
Weight,  pounds.  
Ratio  to  weight  of  piece. 
Pressure  in  powder-cham- 
ber, Ibs.  per  square   inch 
Muzzle  velocity,  ft.  -sees.  .. 
Muzzle  energy,  foot-  tons.. 
Penetration  in  steel: 
Muzzle,  inches  
3500  yards,  inches  

38.000 

2,IOO 

30,570 
27.1 

20.6 

37,000 
i,975 
64,084 

33-8 
27  5 

27.500 

I,O2O 

5,770 

8.2 

a  U.R.     brown   prismatic,     b  W.H.  brown  prismatic,     c  V. P.  brown  prismatic.     </ brown 
prismatic;  e  V.M.  brown  prismatic. 


272  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

and  hence  any  tendency  of  the  block  to  rotate  is  overcome. 
When  the  block  reaches  the  end  of  its  travel,  it  strikes 
against  the  ends  of  the  guide-rails  and  releases  the  tray- 
latch  from  its  recess  in  the  breech  by  the  shock,  as  before 
explained.  As  the  block  is  not  able  to  move  further  on  the 
tray,  but  is  free  to  swing  with  the  tray  around  the  pin  d,. 
the  pressure  of  the  teeth  of  c  against  those  of  the  rack  will 
cause  this  swinging  to  take  place,  thus  opening  the  breech 
for  loading. 

A  reversal  of  these  motions  closes  the  breech  for  fir- 
ing. 

The  table  on  page  271  gives  the  details  with  reference  to 
the  seacoast  guns  and  mortars  in  the  U.  S.  service. 

151.     Old  Guns  in   IT.   S.   Service— 3-inch  Wrought-iron   Rifle— 
4.5-inch  Siege-gun— 4.2-inch  Parrott  Siege-gun— 8-inch  Con- 
verted Rifle — 15-inch  Rodman  Smooth-bore. 
3-iNCH  WROUGHT-IRON  RIFLE  (Fig.  141).— This  gun  was 
used  during  the  war  of  1861-65,  and  is  still  found  in  service. 

n It  is  made  by  wrapping  boiler- 

~'ri^"^-""J"-"-"I-Jl"'Z"Z!]    iron   around    a    wrought- iron 
LJ  mandrel,  heating  the  resulting 

FlG-  I4I-  cylinder  to  a  welding-heat,  and 

passing  it  through  the  rolls.  The  gun  is  then  bored,  turned, 
and  rifled.  The  object  of  the  construction  is  to  have  the 
fibres  of  the  wrought  iron  in  the  direction  of  the  tangential 


FIG.  142. 

stress.     The  objection  to  the  construction  is  the  liability  to 
false  welds. 

4.5-iNCH  SIEGE-GUN  (Fig.  142). — This  gun  is  made  of  cast 
iron,  cast -solid,  and  bored,  turned,  and  rifled.  It  has  given 
very  good  results,  but  is  uncertain  in  strength,  like  all  guns 


GUNS. 


cast  on  this  plan,  and  several  accidents  have  occurred  which; 
have  caused  it  to  be  abandoned. 

4.2-iNCH  PARROTT  SIEGE-GUN  (Fig.  143). — This  gun  is 
also  made  of  cast  iron,  but  is  reinforced  at  the  breech  by  a: 


FIG.  143. 

heavy  jacket  of  wrought  iron.  This  jacket  was  made  by 
coiling  a  hot  bar  of  wrought  iron  around  a  mandrel  into  a 
spiral,  and  welding  the  coils  into  a  cylinder  by  blows  from  a 
hammer  parallel  to  the  axis  of  the  cylinder.  The  cylinder 
was  next  bored,  and  then  shrunk  upon  the  exterior  of  the 
breech  of  the  gun.  At  the  time  these  guns  were  made, 
nothing  was  known  about  the  theory  of  shrinkage  as  at  pres- 
ent applied  to  guns,  and  hence  the  shrinkage  was  not  prop- 
erly regulated,  and  was  very  often  a  source  of  weakness, 
especially  at  the  junction  of  the  front  end  of  the  cylinder 
with  the  gun.  In  spite  of  this,  however,  these  guns  have 
proved  very  serviceable. 

8-iNCH  CONVERTED  RIFLE  (Fig.  144). — These  guns  were 
made  for  the  purpose  of  utilizing  a  large  number  of  old  10- 


FIG.  144- 


inch  Rodman  cast-iron  guns  which  were  on  hand,  the  idea 
being  to  render  them  more  accurate  and  powerful,  by  con- 
verting them  into  rifled  guns.  This  was  done  by  boring 
out  the  10-inch  gun  to  a  larger  diameter,  and  inserting 


o?  -no 


2/4  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY.  ' 

a  tube  into  this  bore.  This  tube  was  held  in  place  by  a  col- 
lar, a,  screwed  into  the  cast-iron  body  and  resting  against  a 
shoulder,  b,  on  the  muzzle  end  of  the  tube.  The  tubes  were 
made  at  first  by  coiling  bars  of  wrought  iron  around  a  man- 
drel, and  welding  them  by  axial  blows.  This  method  was 
abandoned  on  account  of  the  false  welds  in  the  tube,  which 
sometimes  cracked  and  separated  from  this  cause.  The 
tubes  were  finally  made  of  steel,  and  numbers  of  these  guns 
are  still  in  service.  The  rotation  of  the  tube,  due  to  the  ac- 
tion of  the  projectile,  is  prevented  by  a  pin,  c,  which  passes 
through  the  cast  iron  body  and  enters  the  tube. 

15-iNCH  RODMAN  SMOOTH-BORE. — This  gun  is  still  re- 
tained in  service,  and  is  intended  to  be  used  with  large 
charges  of  mammoth  powder,  as  a  secondary  gun,  for  com- 
paratively short  ranges,  and  against  light  armor.  It  is 
cast  hollow  on  the  Rodman  plan;  its  projectile  weighs  450 
pounds,  and  the  gun  about  22  tons. 

152.  Foreign  Guns — Krupp  Mechanism — Locking-screw. 

All  heavy  guns  are  built  upon  the  same  principles  as 
those  already  explained,  and  hence  a  description  of  the  guns 
of  different  countries  is  unnecessary.  The  only  departure 
from  the  system  above  described,  is  in  the  case  of  the  breech 
mechanism. 

KRUPP  MECHANISM. — While  the  French  or  interrupted- 
screw  system  has  been  adopted  by  most  of  the  foreign  na- 
tions, Germany,  and  some  others,  use  the  Krupp  system. 

It  has  stood  the  test  oi  service  and  has  been  well  and 
favorably  known  for  many  years,  and  hence  will  be  described 
here. 

The  jacket  a,  Fig.  145,  extends  to  the  rear  of  the  tube, 
and  carries  the  fermeture.  A  slot  is  cut  transversely  in  the 
jacket  just  in  rear  of  the  tube.  This  slot,  in  front,  is  perpen- 
dicular to  the  axis  of  the  bore,  and  is  a  plane  surface,  with 
corners  rounded  to  avoid  sharp  angles.  In  rear,  the  sur- 
face of  the  slot  is  cylindrical,  and  the  axis  of  the  cylinder  is 
inclined  to  that  of  the  bore.  Two  guides,  bb' ,  are  parallel 
to  the  axis  of  the  cylinder.  In  this  slot  slides  a  breech- 
block, k,  whose  shape  corresponds  to  that  of  the  slot.  It 


G  UNS. 


has  two  recesses  for  the  guides  bb' ,  and  in  the  upper  face, 
a  third  recess,  in  which  rests  a  long  screw  c,  called  the 
translating-screw.  This  screw  is  held  in  two  collars  in  the 
breech-block,  and  works  in  a  half-nut,  d,  on  the  gun.  When 
the  screw  c  is  turned  by  a  wrench,  such  as  e,  the  block  is 
drawn  out  of  its  recess  or  pushed  home. 

LOCKING-SCREW. — In  order  to  obtain  a  rapid  motion  in 
opening  and  closing  the  breech,  the  screw  c  is  cut  with  a 
quick  pitch.  Consequently, 
there  is  very  little  power  to 
press  the  gas-check  firmly 
home,  or,  in  opening  the 
breech,  to  overcome  any  stick- 
ing that  may  occur.  It  is 
also  necessary  to  have  some 
method  of  locking  the  breech- 
block to  the  jacket  in  firing, 
to  prevent  accident. 

All  these  objects  are  ac- 
complished by  the  locking 
mechanism.  This  consists  of 
a  nut,  f,  and  a  screw,  g.  The 
nut  has  a  series  of  rings,  r, 
formed  on  its  exterior  sur- 
face. The  outer  ring  is  com- 
plete, the  others  are  partially 
cut  away.  When  the  nut  is 
turned  so  that  the  cut-away 
portions  of  the  rings  are  in 
rear,  the  surface  of  the  nut 
coincides  with  that  of  the  rear 
of  the  block.  When  turned 
the  parts  of  the  rings 


120^ 


FIG.  145. 
in   the   breech. 


not  cut  away  project  beyond 

the   block   and   enter   corresponding    cuts 

The  nut  has  a  small  amount  of  travel  along  its  screw  g. 

Action— -The  translating-screw  c  leaves  the  block  not 
quite  forced  home.  The  nut /is  at  the  bottom  of  its  recess 
in  the  block,  nearest  the  axis  of  the  gun,  and  the  cut  rings 


276 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


of  the  nut  are  turned  to  the  rear.  The  wrench  e  is  now 
applied  to  the  screw  g  and  the  screw  turned.  This  will 
cause  the  nut /to  move  along  the  screw,  it  being  unable  to 
turn  because  of  the  cut  parts  of  the  rings  bearing  on  the 
back  of  the  transverse  slot  in  the  breech.  As  soon,  how- 
ever, as  the  rings  come  opposite  the  cuts  in  the  breech,  the 
nut  will  turn,  its  rings  entering  the  corresponding  cuts  in 
the  breech,  and  after  turning  120°,  the  pin  h  bears  against 
a  shoulder  on  the  block,  and  stops  the  rotation  of  the  nut. 
As  the  screw  still  turns,  H:he  effect  will  be  to  cause  the  rings 
to  bear  against  the  cuts  in  the  breech,  and  thus  force  the 
block  home.  At  the  same  time  the  rings  bearing  in  the 
cuts  lock  the  block.  A  reversal  of  these  operations  opens 
the  breech. 

153.  The   Gas-check  —  General  Features   of  the   Mechanism — Ad- 
vantages and  Disadvantages. 

GAS-CHECK. — With  the  Krupp  mechanism,  it  is  evident 
that  neither  the  De  Bange  nor  the  Freyre  gas-checks  can  be 

used,  since  both  of  them  must  be 
drawn  back  from  their  seats  in  the 
gun,  being  attached  to  the  breech- 
block. The  Krupp  block  slides 
across  the  breech,  and  hence  it  is  nec- 
essary to  use  a  gas-check  which  can 
be  left  in  the  gun.  The  Broadwell 
ring  is  used.  It  consists  (Fig.  146) 
of  two  parts  :  the  obturating-ring, 
a,  and  the  obturator-plate,  b.  The 
exterior  surface,  cc?,  of  the  ring  is 
spherical,  so  that  it  can  be  readily 
seated  in  the  gun,  and  returned  to 
its  place  if  it  should  become  un- 
FlG-  T46.  seated.  The  surface  c'd  is  plane, 

with  a  series  of  grooves  to  act  as  an  air-packing,  as  before 
explained,  and  also  to  collect  any  dirt  that  may  be  on  the 
surface  of  the  obturator-plate.  The  obturator-plate  b  is  of 
hardened  steel,  and  is  fitted  into  the  face  of  the  breech- 
block. The  hollow  e  collects  fouling,  which,  if  the  whole 


BREECH  BLOCK. 

TUBE 

C' 

;  ( 

^^ 

—  — 

-C 

d' 
b 

a 

e 

b 

r 

•^-  — 
~~*~* 

1 

GUNS.  277 

front  surface  were  plane,  would  be  drawn  against  the  edge 
of  the  obturating-ring  when  the  block  is  withdrawn,  and 
thereby  increase  the  liability  to  fouling  of  the  surface  c'd. 
The  surfaces  c'c  and  c'd  are  those  which  must  be  kept  sealed 
against  the  escape  of  gas.  The  surface  c'd  is  especially 
difficult  to  seal,  and  hence  the  necessity  for  the  heavy  press- 
ure given  by  the  locking-screw,  to  set  the  obturator-plate 
firmly  against  the  ring. 

Action. — The  gas  acts  upon  this  ring  to  force  the  thin 
edge  c  against  the  walls  of  the  bore,  and  also  to  press  the 
ring  backwards  against  the  obturator-plate,  forcing  down 
especially  the  edge  d. 

GENERAL  FEATURES  OF  MECHANISM. — The  locking- 
screw  just  described  is  supported  at  its  outer  extremity 
by  a  plate,  k,  Fig.  145,  called  the  locking-plate.  The 
travel  of  the  block  is  limited  by  a  chain,  or  by  a  stop-bolt 
which  passes  through  the  upper  part  of  the  breech,  and 
projects  into  a  groove  in  the  block.  The  jacket  is  bored 
out  in  prolongation  of  the  bore,  for  the  insertion  of  the 
projectile  and  charge  in  loading,  and  this  hole  is  also 
made  through  the  breech-block,  so  that  when  the  block 
is  withdrawn  the  hole  through  it  is  also  in  prolongation 
of  the  bore.  The  rounded  shape  of  the  rear  of  the  block, 
and  of  the  slot,  gives  strength  by  avoiding  sharp  corners, 
and  the  inclination  of  the  axis  of  the  cylinder  to  that  of 
the  bore,  with  that  of  the  guides,  gives  a  component  mo- 
tion of  the  block  parallel  to  the  axis  and  gradually  seats 
the  block  firmly,  while  by  a  slight  motion  outward,  all 
the  parts  become  free  and  the  block  is  easily  with- 
drawn. 

ADVANTAGES. — The  Krupp  mechanism  is  very  simple 
and  not  liable  to  get  out  of  order.  It  has  been  thoroughly 
tested,  and  found  to  be  reliable.  If  it  becomes  stuck  or 
wedged  in  the  gun,  it  may  be  more  easily  removed  than  the 
screw,  as  it  is  more  accessible. 

DISADVANTAGES. — It  requires  a  heavier  forging  for  its 
jacket  than  the  screw  system,  and  consequently  increases 
-the  weight  of  the  gun  for  the  same  -length  of  bore.  The 


2/8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Broadwell  ring  is  not  as  good  a  gas-check  as  the  De  Bange 
or  Freyre. 

The  longitudinal  stress  is  not  uniformly  distributed  over 
the  cross-section  of  the  jacket,  and  this  is  seen  by  a  ten- 
dency of  the  gas-check  seat  to  become  oval,  the  longer  axis, 
being  parallel  to  that  of  the  slot. 

It  is  more  exposed  to  a  front  fire  when  open. 

It  tends  to  guillotine  the  cartridge. 


CHAPTER   IV. 

PROJECTILES   AND   ARMOR. 

PROJECTILES. 

154.  Classification — Solid  Shot— Chilled  Shot— Steel  Shot. 

CLASSIFICATION. — Projectiles  may  be  classified  according- 
to  their  structure,  as  solid  shot,  shell,  and  case-shot ;  accord- 
ing to  their  use,  into  field,  siege,  and  sea-coast  projectiles ; 
and  according  to  their  shape,  as  spherical  and  oblong. 

Spherical  projectiles  are  now  obsolete. 

SOLID  SHOT. — Solid  shot  were  formerly  used  for  armor- 
piercing,  and  are  still  used  in  small  arms  against  animate 
objects.  The  advantages  of  solid  shot  are,  that  they  have 
greater  weight  for  the  same  volume,  and  hence  greater 
energy  for  a  given  velocity  ;  and  where  it  is  necessary  to 
concentrate  energy  upon  a  given  area,  as  in  attacking  an 
armor-plate,  they  were  generally  employed. 

The  disadvantages  are  that  for  attacking  armor,  the  pro- 
jectile must  possess  great  hardness  to  penetrate,  and  great 
toughness  to  resist  breaking  up  on  impact,  and  if  the  shot 
be  made  solid,  it  is  subjected  to  initial  strains  due  to  casting 
or  forging,  which  cannot  be  removed  ;  the  metal  in  the  in- 
terior is  not  sound,  and  hence  we  obtain  weaker  projectiles 
when  solid  than  when  they  have  an  interior  cavity  or  core. 
This  cavity  removes  the  unsound  metal,  if  the  projectile  is 
of  cast  iron,  or  if  of  steel,  allows  it  to  be  treated,  so  that  the 
strains  can  be  removed  and  toughness  attained.  Such  shot 
are  generally  called  "  cored  shot." 

The  only  solid  projectiles  at  present  in  general  use  are  for 
small  arms. 

279 


28o 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


CHILLED  SHOT. — With  the  introduction  and  improve, 
jnent  of  wrought-iron  armor,  cast-iron  projectiles  became 

useless,  as  they  were  broken 
on  impact.  This  led  to  the 
introduction  of  chilled  cast- 
iron  projectiles.  The  Palliser 
projectile,  so  called  from  its 
inventor,  Major  Palliser  of 
the  British  Army,  was  for  a 
long  time  quite  celebrated, 
and  very  effective  against 
wrought-iron  armor. 
FIG.  147.  It  was  made  by  casting 

the  ordinary  cored  shot  in  a  chill,  Fig.  147. 

The  body  of  the  projectile  is  cast  in  sand  to  give  tough- 
ness, and  the  head  in  a  cast-iron  mould  or  chill  a,  so  called 
because  it  carries  off  the  heat  of  the  parts  in  contact  with  it 
so  rapidly  as  to  cause  chilling,  and  produce  great  hardness. 
The  exterior  of  this  chill  conforms  generally  to  the  shape 
of  the  head,  to  insure  uniform  cooling,  and  it  is  lined  with  a 
movable  lining,  b. 

The  latter  soon  becomes  worn  from  contact  with  the 
heated  metal,  and  is  removed  and  replaced  by  a  new  lining, 
thus  preserving  the  body  of  the  chill  a.  The  head  of  the 
chilled  shot  is  shown  at  c. 

STEEL  SHOT. — As  armor  improved  in  its  resisting  quali- 
ties, the  chilled  cast-iron  projectile  was  broken  on  impact,  and 
steel  shot  were  substituted.  The  best  of  these  are  made  of 


12  "INCH  ARMOR  PIERCING  SHOT. 
FORGED  STEEL. 


FIG.  148. 


chrome  steel,  forged  and  tempered.  Two  processes,  known 
as  the  Holtzer  and  Firminy,  are  so  far  the  best,  but  they  are 
secret,  and  nothing  is  known  of  them.  The  projectiles  made 


PROJECTILES  AND   ARMOR.  28 1 

by  these  processes  give  the  best  results  when  used  against 
modern  steel  armor,  but  they  are  very  expensive,  and  hence 
attempts  are  now  being  made,  with  some  appearance  of 
success,  to  replace  them  by  cast-steel  projectiles,  which  are 
tempered  by  a  secret  process. 

Fig.  148  shows  a  forged-steel  Holtzer  armor-piercing 
cored  shot. 

155.  Shell — Definition — Shell  for  Sea-coast  Service — Deck-piercing 
Shell. 

DEFINITION. — A  shell  is  a  hollow  projectile,  containing  a 
bursting  charge  of  gunpowder,  or  some  high  explosive,  and 
a  fuze  to  ignite  this  charge  at  some  point  of  its  flight,  or 
upon  impact. 

Shells  are  used  in  the  sea-coast,  siege,  and  field  services, 
and  their  construction  depends  on  the  purpose  for  which 
they  are  intended. 

SHELLS  FOR  SEA-COAST  SERVICE. — In  the  sea-coast  ser- 
vice, shells  are  used  in  high-powered  guns  for  attacking 
armor,  or  in  mortars  with  high  angle-fire  for  piercing  the 
decks  of  vessels. 

Against  Armor. — If  the  shells  can  be  made  strong  enough 
to  penetrate  armor,  they  are  preferred  to  shot,  because  they 
burst  after  penetration,  and  acting  in  a  confined  space  on  a 
ship,  cause  great  destruction.  For  this  purpose  the  walls  of 
the  shell  must  be  strong,  and  hence  the  cavity  small.  The 
cavity  being  small,  will  not  contain  a  large  bursting  charge 
of  powder,  and  the  walls  of  the  shell  being  strong,  the  gases 
from  this  charge  may  not  develop  sufficient  pressure  to  rup- 
ture them. 

On  this  account,  and  because  of  its  greater  destructive 
effect,  a  high  explosive  as  a  bursting  charge  is  necessary. 

Gun-cotton  has  been  tried  as  a  bursting  charge  for  these 
shells.  While  it  has  given  good  results  in  some  cases,  it  is 
liable  to  premature  explosion  from  shock  and  friction,  and 
if  desensitized  by  moisture  or  by  paraffine,  it  requires  a 
strong  primer  of  dry  gun-cotton  to  detonate  it,  and  this 
primer  is  liable  to  detonation  by  shock.  The  same  principle 
applies  to  nearly  all  the  high  explosives  which  have  been 


282 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


tried,  and  hence  the  problem  of  a  suitable  high  explosive 
for  armor-piercing  shell  is  not  yet  solved.  This  has  led  to 
the  introduction  of  various  methods  of  firing  high  explosives^ 
as  the  pneumatic  dynamite  gun,  etc. 

With  armor-piercing  shell,  it  is  sought  by  various  means 
to  delay  the  action  of  the  bursting  charge  till  penetration  is 
complete,  as  by  wrapping  the  charge  in  flannel,  using  de- 
layed-action fuzes,  etc. 

AGAINST  THE  DECKS  OF  VESSELS. — The  problem  of  pen- 
etrating the  sides  of  armored  vessels  being  so  difficult,  at- 
tempts are  made  to  perforate  their  decks.  When  the  weight 
of  guns,  machinery,  and  armor  carried  by  ships  of  the  pres- 


.I2JNCH  DECK  PIERCING  SHELL. 
"FORGED  STEEL. 


FIG.  149. 

ent  day  is  considered,  the  available  weight  left  for  deck  pro- 
tection is  comparatively  small,  and  hence  a  thickness  of  about 
4^  inches  of  protective  deck  is  about  all  that  can  be  carried. 
Against  these  decks,  the  vertical  fire  of  shell  from  heavy 


CAST  IRON  SHELL  TOR  12  INCH  MORTAR. 


FIG.  150. 

rifled  mortars  is  directed.  The  shells  for  these  mortars  do 
not  require  great  strength  of  wall,  since  the  thickness  to  be 
penetrated  is  so  small,  and  hence  they  may  be  made  of  cast 
iron,  with  great  interior  capacity.  They  carry  heavy  burst- 
ing charges,  and  their  effect  is  very  destructive.  The  dis- 
advantage is,  the  difficulty  of  hitting  the  object.  As  the 
shells  are  fired  with  comparatively  low  charges,  the  dangers 


PROJECTILES  AND   ARMOR.  283 

of  premature  explosion  from  shock  are  lessened,  and  recent 
experiments  at  Sandy  Hook  have  shown  that  high  explo- 
sives can  be  fired  from  these  mortars  with  safety.  At  pres- 
ent these  shells  are  made  of  forged  steel. 

Figs.  149  and  150  show  a  steel  deck-piercing  shell  and  a 
cast-iron  shell  for  the  1 2-inch  mortar. 

156.  Siege  Shell— Field  Shell. 

SIEGE  SHELL. — The  shells  for  siege  purposes  are  some- 
what similar  to  those  for  deck  piercing.  They  are  used  in 
direct  and  curved  fire,  and  against  earth  or  masonry.  Their 
object,  therefore,  is  to  displace  the  earth  and  masonry,  and 
as  no  great  strength  is  required  against  these  obstacles,  the 
siege-shell  are  made  of  cast  iron.  In  firing  against  masonry, 
it  is  necessary  not  only  to  penetrate,  but  also  to  remove  the 
broken  fragments,  so  that  the  next  shot  may  fall  upon  a 
fresh  surface.  For  this  purpose  large  bursting  charges  are 
required,  and  hence  large  cavities,  and  comparatively  thin 
walls.  Very  long  shell  are  sometimes  supplied  for  this  pur- 
pose, and  are  called  "  torpedo  shell." 

Against  earth,  the  maximum  displacement  is  required, 
and  some  experiments  made  with  gun-cotton  as  a  bursting 


5  INCH  SIEGE  SHELL 
CAST  IRON. 


FIG.  151. 

charge  show  that  it  is  very  effective.  The  5-inch  siege  shell 
is  shown  in  Fig.  151. 

FIELD  SHELL. — In  field  artillery  the  objects  to  be  at- 
tacked have  little  resistance,  as  they  are  generally  light  field 
entrenchments,  buildings,  or  troops,  and  hence  the  effect 
depends  on  the  number  of  fragments  into  which  the  shell 
bursts. 

The  number  of  these  fragments  will  depend  on  the 
brittleness  of  the  material,  and  the  pressure  of  the  gases 


284  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

from    the    bursting    charge,    at    the    time    when    rupture 
occurs. 

The  natural  tendency  of  a  shell  is  to  burst  in  a  meridian 
plane,  or  a  plane  through  its  longer  axis,  since  the  total 
pressure  of  the  gases  normal  to  this  plane  is  greater  than 
that  normal  to  the  transverse  plane.  If  the  pressure  of  the 
gases  is  developed  slowly,  as  from  a  bursting  charge  of 
large-grained  powder,  rupture  will  occur  as  just  indicated, 
and  we  will  have  a  few  large  fragments,  and  the  effect  will 
be  limited.  To  avoid  this  it  is  necessary — 

1.  To  use  as  a  bursting  charge,  fine-grained  powder  of 
high  gravimetric  density.     By  this  means  the  pressure  is 
rapidly  developed,  and  the  largest  possible  weight  of  charge 
is  contained  in  a  given  volume. 

2.  To  prevent  rupture  in  a  longitudinal  plane,  the  interior 
of  the  shell  is  sometimes  grooved  spirally,  to  weaken  it,  and 
give  more  fragments.     A  remaining  velocity  of  500  ft.-secs. 
is  generally  considered  sufficient  to  disable  or  kill  a  man, 
and  a  fragment  weighing  about  I  ounce  with  this  velocity 
is  effective.     With   the   13.5-lb.  shell  this  would  give  216 
effective  fragments,  and  with  the  20  Ib.  shell  320.     In  prac- 
tice these  results  cannot  be  obtained. 

Owing  to  the  irregularity  of  their  action,  field-shells  are 
seldom  used  against  animate  objects,  except  at  very  long 
distances,  or  when  under  cover.  They  are  used,  however, 
with  percussion  fuzes,  to  obtain  the  range  quickly.  By 

firing  a  percussion  shell  with  a 
certain  elevation,  so  as  to  strike  in 
front  of  the  target,  and  again  with 


3  20  INCH  flCLD  SHCLL       , 

CAST  IRON     ^^      an   increased    elevation,   so   as   to 


FIG.  152.  strike    beyond    it,    and    observing 

the  points  of  burst,  the  target  is 

thus  enclosed  in  a  fork,  and  by  working  between  these  lim- 
its, the  true  elevation  is  soon  obtained.  The  3.2-inch  shell  is 
is  shown  in  Fig.  152. 

157.  Case-shot — Grape — Canister. 

DEFINITION. — Case-shot  may  be  defined  to  be  a  collec- 
tion of  particles  enclosed  in  a  case  or  envelope,  the  latter 


PROJECTILES  AND   ARMOR. 


285 


3   a 


being  intended  to  rupture  in  the  gun,  or  at  some  point  in 
flight,  and  liberate  the  enclosed  particles. 

According  to  the  place  of  rupture  of  the  envelope,  case- 
shot  may  be  divided  into — 

1.  Grape  ; 

2.  Canister, 

whose  envelope  is  broken  in  the  gun,  by  the  shock  of  dis- 
charge ;  and, 

3.  Shrapnel, 

whose  envelope  is  broken  at  some  point  of  the  flight  of  the 
projectile. 

GRAPE. — This  projectile  is  no  longer  used,  but  is  interest- 
ing historically.  It  consists  of  three  layers  of  balls,  each 
layer  containing  generally  three  balls  (see 
Fig.  153)  held  in  place  by  top  and  bottom 
plates,  a  and  b,  of  iron ;  a  central  bolt  and 
nut,  c  ;  and  two  intermediate  rings,  dd.  It 
was  used  in  the  sea-coast  service  with 
smooth-bore  guns,  against  the  masts  and 
rigging  of  ships,  and  against  men ;  also  in 
the  siege  and  field  services  against  ani- 
mate objects  in  mass,  at  distances  too 
great  for  smaller  projectiles. 

CANISTER.  —  This  con- 
sists (Fig.  154)  of  a  number  of  spherical  bullets 
of  lead  hardened  with  antimony,  or  of  cast 
iron,  contained  in  a  can;  hence  the  name. 
The  envelope  is  closed  by  a  top  and  bottom 
plate  of  iron,  and  is  intended  only  for  conven- 
ience in  transportation,  and  in  loading. 

It  was  used  principally  in  the  field  service 
with  the  old  smooth-bore  guns,  against  ani- 
mate objects  at  close  range. 

In  both  these  projectiles,  the  case  rup- 
tured in  the  bore,  and  the  projectiles  scattered  at  the  muz- 
zle, forming  a  cone  of  dispersion,  with  its  apex  at  the  latter 
point. 

For  rifled  guns  it  was  necessary  to  prevent  the  case 
taking  the  grooves,  and   thus  giving  it  the  rifled   motion 


mm 
FT  ) 


d 


d 


FIG.  153. 


FIG.  154. 


286 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


and   increasing   the    lateral   dispersion    of    the    projectiles, 
which  r\vas  already  great. 

For  this  purpose  the  case  was  made  stronger, 
since  with  the  tin  case,  the  projectiles  were  forced 
sidewise  by  the  shock  of  discharge,  expanding 
the  case,  and  forcing  it  into  the  grooves.     In  our 
service  this  was  done  by  adopting  the  Sawyer 
canister,  the  case  of  which  is  made  of  malleable 
cast  iron,  weakened  by  spiral  cuts,  as  shown  in 
Fig.  155,  so  as  to  insure  its  breaking  up  in  the  gun. 
All  these  projectiles  were  used  at  short  range, 
and  since  the  fighting  range  has  been  increased, 
owing  to  the  longer  range  and  higher  ballistic 
FIG.  155.     power  of  small  arms,  they  are  little  used  at  the 
present  day.     A  few  rounds  of  canister  are  sometimes  car- 
ried with  the  field  gun  for  emergencies. 

158.  Shrapnel — Cone  of  Dispersion — Causes  which  Affect  it. 

SHRAPNEL. — This  projectile  is  now  the  most  important  in 
field  artillery,  and  is  employed  to  the  exclusion  of  all  others. 
It  consists  essentially  of  a  case  or  envelope  containing  small 
round  projectiles,  and  a  bursting  charge,  and  fuze.  The 
charge  is  sufficient  to  rupture  the  envelope  at  a  given  point 
of  flight  of  the  projectile,  the  fuze  being  arranged  to  ignite 
the  charge  at  that  point.  After  the  rupture  of  the  envelope, 
the  contained  projectiles  move  on  with  a  velocity  which  is 
the  resultant  of  that  due  to  discharge,  and  to  the  bursting 
charge,  and  act  from  the  point  of  burst  to  the  target,  as 
canister.  The  object  of  the  envelope  then  is  to  convey  the 
small  projectiles  to  within  striking  distance  of  the  target, 
where  they  are  liberated,  and  each  particle  acts.  The  pro- 
jectile is  used  entirely  against  animate  objects,  and  its  advan- 
tages over  the  shell  are  that  the  division  of  the  particles  is 
made  beforehand,  and  each  one  is  of  the  proper  size  to  exert 
a  disabling  or  killing  effect. 

CONE  OF  DISPERSION. — When  rupture  of  the  case  occurs, 
each  contained  particle  describes  its  own  path,  and  the 
paths  thus  described,  taken  together,  form  the  elements  of 
the  "  cone  of  dispersion."  The  intersection  of  this  cone  with 


PROJECTILES  AND   ARMOR.  287 

the    ground  is   an  irregular   oval,  and    its   area  will  vary 
with — 

CAUSES  WHICH  AFFECT  IT.— i.  The  angle  of  elevation  of 
the  piece ; 

2.  The  velocity  of   translation   of   the   shrapnel  before 
bursting ; 

3.  The  velocity  of  rotation  of  the  shrapnel  before  bursting; 

4.  The  position  of  the  bursting  charge ; 

5.  The  height  above  the  ground  at  which  the  shrapnel 
bursts. 

Angle  of  Elevation. — If  this  be  large,  other  things  being 
equal,  the  angle  of  fall  will  be  large,  and  the  plane  of  inter- 
section being  more  nearly  normal  to  the  mean  axis  of  the 
cone  of  dispersion,  the  area  of  the  oval  will  decrease ;  the 
converse  is  true  for  small  angles  of  elevation  (see  Fig.  156). 


FIG.  156. 

Velocity  of  Translation. — The  greater  this  velocity,  the 
greater  will  be  the  velocity  of  the  particles  in  the  plane  of 
fire,  and  consequently  the  longer  the  oval  in  this  direction. 

Velocity  of  Rotation. — This  causes  the  particles  to  move 
at  right  angles  to  the  plane  of  fire,  and  hence  increases  the 
lateral  dispersion  of  the  particles,  and  the  width  of  the  oval. 

Position  of  Bursting  Charge. — This  may  be  in  front,  or  in 
rear  of  the  particles.  If  in  front,  it  decreases  the  velocity 
of  translation  of  the  particles,  and  hence  decreases  the  length 
of  the  oval,  and  for  this  reason  its  effect  is  injurious.  For 
other  reasons,  however,  the  position  is  a  good  one,  as  will 
be  seen. 

When  in  rear,  it  increases  the  velocity  of  the  particles  in 
the  plane  of  fire  ;  but  there  are  objections  to  this  position. 

Height  of  Burst. — It  is  evident  that,  for  a  given  inclina- 
tion, and  for  given  velocities  in  the  plane  of  fire  and  later- 


288 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


ally,  the  higher  the  point  of  burst,  the  greater  the  area  of 
the  oval. 

The  constant  tendency  with  shrapnel  is  to  increase  the 
velocity  of  the  particles  in  the  plane  of  fire,  and  to  decrease 
that  at  right  angles  to  this  plane ;  and  the  best  possible  con- 
dition for  the  efficiency  of  this  projectile  is  when  the  area 
of  the  oval  is  such  that  each  bullet  will  hit  a  man.  The 
best  position  for  the  point  of  burst  is  about  6  yards  above 
and  50  yards  in  front  of  the  target. 

159.  Construction  of  Spherical  Shrapnel — Early  Shrapnel — U.  S. 
Spherical  Case — Boxer  Spherical  Shrapnel. 

Spherical  shrapnel  is  now  obsolete,  but  the  history  of 
its  development  shows  clearly  the  directions  in  which  im- 
provements have  been  made. 

EARLY  SHRAPNEL, — The  projectile  was  invented  by 
Colonel  Shrapnel  of  the  British  Army,  about  1803.  In  its 
early  form  it  was  simply  a  spherical  shell  filled  with  bullets, 
and  the  bursting  charge  was  contained  in  the  interstices  be- 
tween them.  The  objections  to  this  arrangement  were  : 

1.  When  the  projectile  was  fired  the  balls  spread  side- 
wise,  and  tended  to  deform  or  burst  the  shell.     Hence  the 
latter  was  made  with  thick  walls  to  resist  this  force,  and 
this  decreased  the  interior  capacity,  and  consequently,  the 
number  of  bullets  which  it  would  contain. 

2.  The  powder,  being  loose  among  the  bullets,  was  sub- 
jected  to  trituration  and   friction  in   handling,   and   hence 
was  liable  to  accident.     Since  the  space  between  the  bullets 

was  large,  the  density  of  loading  of 
the  bursting  charge  was  low,  and 
hence  a  large  bursting  charge  was 
required  to  rupture  the  envelope. 
This  scattered  the  fragments  too 
much,  and  rendered  the  action  of  the 
fuze  more  irregular. 

U.  S.  SPHERICAL  CASE.  —  These 
defects  suggested  the  improvements 
which  were  made  in  the  spherical, 
the  Civil  War  (Fig.  157): 


FIG.  157. 
shrapnel  used  durin: 


PROJECTILES  AND   ARMOR.  289 

1.  To  prevent  the  spreading  of  the  bullets,  the  shell  was 
first  filled  with  them,  and  melted  sulphur  was  then  poured 
in,  filling  the  interstices  between  the  bullets.     They  were 
thus  converted  into  a  solid  mass,  and  as  their  tendency  to 
spread    siclewise  was   thus   destroyed,  the   case  was   made 
thinner,  and  consequently  held  more  bullets. 

2.  To  diminish  the  bursting  charge,  a  cylindrical  hole 
was  bored  through  the  bullets  and  sulphur,  and  in  this  the 
bursting  charge  was  placed.     Thus  the  density  of  loading 
was  increased,  and  a  small  bursting  charge  could  be  used 
with  less  uncertainty  in  the  action  of  the  fuze. 

The  objections  to  this  arrangement  were  that  the  sul- 
phur caused  the  bullets  to  stick  together,  and  prevented 
their  separation  after  the  bursting  of  the  case,  and  that  the 
effect  of  the  bursting  charge  was  to  increase  the  lateral 
dispersion  of  the  particles. 

BOXER  SPHERICAL  SHRAPNEL.— Most  of  the  defects  in 
the  above  shrapnel  were  remedied  in  the  Boxer  Spherical 
Shrapnel  (Fig.  158),  invented  by 
Colonel  Boxer  of  the  English  Army. 

In  this  projectile,  the  bursting 
charge  was  placed  in  a  chamber,  a, 
formed  by  .introducing  a  wrought  - 
iron  diaphragm,  b,  into  the  mold  be- 
fore casting,  and  allowing  the  cast 
iron  to  cool  around  it.  The  bullets 

were  introduced   through  the   open- 

,  &  ,  .   ,  FIG.  158. 

ing  c,  the  upper  end  of  which  carried 

the  fuze;  the  flame  from  which  reached  the  charge  through 
a  hole,  d.  The  sulphur  used  as  packing  in  the  U.  S.  shrap- 
nel, was  replaced  by  coal  dust. 

This  shrapnel  possessed  the  following  advantages  : 

1.  The  bullets  did  not  adhere  to  the  matrix  after  burst- 
ing. 

2.  A  small  bursting  charge  could  be  used. 

3.  The  diaphragm  b  weakened  the  case,  so  that  it  would 
burst  readily. 

4.  As  soon  as  the  shrapnel  left  the  piece  (since  its  for- 
ward  portion,  which   contained  the  fuze,  was  lighter  than 


290 


TEXT- BOOK  OF  ORDNANCE  AND    GUNNERY. 


the  rear  portion),  the  lighter  portion  would  turn  to  the  rear, 
leaving  the  centre  of  gravity  in  advance  of  the  centre  of 
figure.  This  brought  the  bursting  charge  in  rear,  and 
hence,  on  explosion,  it  acted  to  increase  the  forward  ve- 
locity of  the  bullets,  and  its  tendency  to  scatter  was  very 
small. 
160.  Oblong  Shrapnel  —  Boxer  —  Modern  Shrapnel  —  Position  of 

Bursting  Charge. 

BOXER  OBLONG  SHRAPNEL. — At  this  point  the  develop- 
ment of  spherical  shrapnel  ceased,  owing  to  the  introduction 
of  rifled  guns  and  oblong  projectiles. 
The  first  oblong  shrapnel  of  any  import- 
ance was  that  of  Colonel  Boxer.  This 
consists  (Fig.  159)  of  a  cast-iron  body,  a  ; 
and  a  wooden  head,  b,  covered  with 
sheet-iron,  c,  riveted  to  the  cast-iron 
body.  The  bursting  charge  is  contained 
in  the  chamber  d  in  rear,  and  over  this 
chamber,  separating  the  charge  from 
the  bullets,  is  a  cast-iron  disk,  e.  The 
central  tube /is  filled  with  powder,  and 
conveys  the  flame  from  the  fuze  g,  to  the 
bursting  charge  d.  The  balls  are  held 
together  by  melted  resin,  and  a  paper 
lining  prevents  the  adhesion  of  the 
matrix  to  the  walls  of  the  envelope. 

This  shrapnel  has  the  following  ad- 
vantages : 

i.  Those  common  to  all  oblong  pro- 
jectiles— of  greater  range  and  accuracy, 


FIG.  159. 


and,  for  a  given  cross-section,  containing  a  larger  number 
of  projectiles  than  the  corresponding  spherical  shrapnel. 

2.  The  charge,  being  in   rear,  acts,  as  with  the  Boxer 
spherical  shrapnel,  to  increase  the  forward  velocity  of  the 
bullets  after  rupture. 

3.  The  head  and  its  attachments,  being  relatively  weak, 
give  way  easily,  and  the  bullets  are  swept  out  to  the  front 
by  the  rear  disk  e\  the  action  in  this  respect  being  like  the 
discharge  of  canister. 


PROJECTILES  AND   ARMOR.  2QI 

The  disadvantages  are : 

1.  The  body  being  of  cast  iron,  the  walls  are  made  com- 
paratively thick  to  withstand  the  shock  of  discharge,  and 
this   reduces   the   interior  capacity,  and  consequently  the 
number  of  bullets  which  the  shrapnel  contains. 

2.  The  wooden  head  takes  up  room  which  can  be  better 
utilized. 

3.  The  delay  caused  by  the  communication  of  fire  from 
the   fuze   to  the  bursting  charge  may   interfere   with  the 
action  of  the   shrapnel,   and   cause  it  to   pass   beyond   its 
proper  point  of  burst  before  exploding. 

4.  The   effect  of   the   pressure   of   the   gases   from   the 
central  tube,  is  to  cause  an  increase  in  the  lateral  spread  of 
the  bullets,  which  is  objectionable. 

MODERN  SHRAPNEL. — These  disadvantages  suggest  the 
improvements  which  have  been  made  in  modern  shrapnel. 
Several  of  these  are  now  under  trial  in  this  country.  The 
following  changes  have  been  made  in  them,  in  comparison 
with  the  Boxer  oblong  shrapnel : 

1.  To  give  sufficient  strength  of  wall  to  withstand  the 
shock  of  discharge,  the  body  is  made  of  drawn-steel  tubing, 
and  the  head  and  base  are  welded  on  by  electricity.     As  this 
is  an  expensive  construction,  wrought-iron  tubing  has  been 
substituted  for  the  steel,  and  the  head  and  base  are  made  of 
cast  iron  screwed  into  the  wrought-iron  body. 

2.  In  case  the  bursting  charge  is  in  front,  as  in  one  of  the 
shrapnel  undergoing   trial,  a  cast-iron   chamber   takes  the 
place  of  the  wooden  head  of  the   Boxer,  and  contains  the 
bursting  charge  and  fuze. 

3.  To  lessen  the  delay  caused  by  communication  of  fire 
through  the  central  tube  to  the  rear  bursting  charge,  this 
tube  is  enlarged,  on  the  interior,  and  made  of  brass  tubing 
so  as  to  give  a  larger  channel  for  the  passage  of  the  flame, 
and  it  does  not  occupy  more  space  in  the  shrapnel,  as  the 
exterior  diameter  of  the  tube  is  not  changed. 

4.  To  prevent  adherence  of  the  balls  after  rupture,  the 
matrix  is  made  of  cast  iron,  indented  so  as  to  hold  the  balls 
in  place  and  form  a  solid  mass  with  the  projectile,  and  yet 


292  TEXT-BOOK  OF  ORDNANCE  AND   GUNNERY. 

so  arranged  as  to  break  up  into  fragments  when  the  shrap- 
nel bursts,  which  add  their  effect  to  that  of  the  balls. 

POSITION  OF  BURSTING  CHARGE. — When  the  bursting 
charge  is  in  front,  we  have  the  following  advantages  : 

1.  It  occupies  less  space  in  the  shrapnel,  since  no  central 
tube  is  required  ; 

2.  It  acts  promptly  to  burst  the  case,  and  hence  the  point 
of  burst  can  be  more  accurately  fixed  ; 

3.  It  occupies  space  in  the  shrapnel  which  it  is  difficult 
to  fill  with  bullets. 

Its  disadvantage  is: 

i.  It  decreases  the  velocity  of  the  fragments  in  the  plane 
of  fire,  instead  of  increasing  it. 

When  the  bursting  charge  is  in  rear,  it  has  the  advan- 
tage: 

i.  It  increases  the  velocity  of  the  fragments  in  the  plane 
of  fire. 

Its  disadvantages  are : 

1.  It  occupies  increased  space  in  the  shrapnel ; 

2.  It  causes  delay  in  bursting  ; 

3.  It  increases  the  lateral  spread  of  the  fragments  ; 

4.  It  is  more  expensive  in  construction. 

For  these  reasons  it  is  probable  that  the  front  charge 
will  be  adopted,  but  it  is  not  yet  settled. 

161.  Description  of  Modern  Shrapnel— Steel- welded— Frankford 
Arsenal. 

STEEL-WELDED. — The  steel-welded  shrapnel  (Fig.  160) 
consists  of  a  steel  tube,  a,  to  which  the  base  b  and  head  c 
are  welded  by  electricity.  The  charge  is  in  rear,  and  is 
separated  from  the  bullets  by  a  disk,  d.  The  central  tube 
communicates  fire  to  the  charge  from  the  fuze.  The  bul- 
lets are  held  in  place  by  a  matrix  of  resin,  melted  and  poured 
in  after  the  former  are  in  place. 

THE  FRANKFORD  ARSENAL.— This  shrapnel  (Fig.  161) 
consists  of  a  wrought-iron  tube,  a,  to  which  the  base  b  of 
cast  iron  is  screwed.  The  rotating  band  c  fits  in  a  groove 
cut  on  the  rear  end  of  the  tube  a.  The  head  d  is  also  of 
cast  iron,  carries  the  bursting  charge  and  fuze,  and  is 


PROJECTILES  AND   ARMOR. 


293 


screwed  to  the  body.  The  bullets  are  held  in  place  by  a 
skeleton  matrix  of  cast  iron,  consisting  of  a  top  and  bottom 
plate,  and  a  series  of  intermediate  plates. 

These  intermediate  plates  are  made  in  segments,  so  that 

the  whole  can  be  built  up  layer 
by  layer,  and  inserted  in  the 
body  of  the  case.  The  head 
and  base  are  then  screwed  on, 
the  band  being  inserted  in  its 
groove  before  the  latter  is 
screwed  home.  This  shrapnel 


-d 


FIG.  160. 


FIG.  161. 


is  much   cheaper  than  the  steel  one,  and  has  given  good 
results  at  the  Proving  Ground. 

The  Hotchkiss  shrapnel  is  similar  to  this. 

162.  Necessity  for  Rotation  of  an  Oblong  Projectile — Energy  of 
Rotation  Required. 

NECESSITY. — It  has  been  shown  that  an  oblong  projec- 
tile when  rotating  about  its  longer  axis,  will  move  through 
the  air  in  the  general  direction  of  that  axis. 

Without  this  motion  of  rotation  about  the  longer  axis,  the 
resultant  resistance  of  the  air,  acting  with  a  certain  lever 


2Q4  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

arm,  will  cause  the  projectile  to  rotate  about  a  short  axis 
through  the  centre  of  mass. 

The  effect  of  this  would  be  to  cause  great  irregularity  of 
motion,  owing  to  the  varying  surface  presented  to  the  air 
by  the  projectile,  during  this  rotation. 

The  rotary  motion  about  the  longer  axis  is  imparted 
to  the  projectile  by  cutting  spiral  grooves  in  the  surface  of 
the  bore,  and  by  placing  a  device  upon  the  projectile  which 
will  fit  in  these  grooves,  and  thus  cause  the  projectile  to 
take  up  the  rifled  motion. 

ENERGY  OF  ROTATION. — The  question  as  to  the  amount  of 
energy  of  rotation  about  the  longer  axis  which  the  projectile 
must  have,  to  enable  it  to  maintain  its  proper  position  dur- 
ing flight,  requires  for  its  determination  analytical  methods 
which  are  too  complex  to  be  given  here.  A  general  discus- 
sion will  show  upon  what  principles  it  depends. 

163.  General  Discussion  of  the  Rotation  of  a  Projectile— Value  of  R. 
The  general  discussion  of  the  motion  of  rotation  of  an  ob- 
long projectile,  based  upon  Euler's  equations,  shows  that  for 
a  projectile  rotating  from  left  to  right,  as  in  our  service,  the 
longer  axis  in  the  time  t  will  deviate  to  the  right  of  the 
plane  of  fire  through  an  angle,  0,  whose  value  is 

Rl 

t  =  tei> •  •  (242) 

in  which  (see  Fig.  162)  R  is  the  resistance  of  the  air  acting 

at  the  centre  of  pressure,  / 
its  lever-arm  with  reference 
to  a  horizontal  axis  through 
the  centre  of  gravity,  /  the 
moment  of  inertia  about  the 
longer  axis  of  the  projectile, 
and  GO  the  angular  velocity  about  the  same  axis'. 

In  order  that  the  projectile  may  be  stable,  Rl  must  be  small 
and  IGO  large.  The  methods  of  decreasing  R  will  be  explained. 
In  order  that  /  may  be  small,  the  centre  of  mass  and  cen- 
tre of  pressure  must  coincide  as  nearly  as  possible.  The  best 
position  for  the  centre  of  mass  is  determined  by  experimen- 


PROJECTILES  AND    ARMOR.  295 

tal  firing,  the  projectile  being  so  weighted  that  this  centre 
can  be  changed. 

To  increase  /,  the  diameter  of  the  projectile  n  ust  be  in- 
creased, its  weight  remaining  constant ;  or  its  mass  or  weight 
may  be  increased,  if  its  dimensions  are  constant,  by  increas- 
ing the  density  of  the  material  of  which  it  is  made. 

GO  may  be  increased  by  giving  a  more  rapid  twist  to  the 
grooves  in  the  gun,  but  this  is  limited  by  the  increased 
strain  brought  upon  the  gun,  and  upon  the  projectile. 

Equation  (242)  shows,  generally  : 

1.  As  /  increases,  0  increases;  and  since  /depends  on  Z, 
the  total  length  of  the  projectile,  if  we  increase  the  length 
of  the  projectile,  we  must  increase  /or  GO,  or  both. 

Therefore  generally  a  long  projectile  must  have  greater 
angular  velocity  about  its  longer  axis,  than  a  short  one  of 
the  same  calibre. 

2.  If  two  projectiles  have  the  same  length  but  different 
diameters,  the  value  of  /  will  be  greater  for  the  larger  pro- 
jectile, and  hence  GO  may  be  less.     That  is,  the  projectile  of 
greater  diameter  will  require  less  angular  velocity  about  its 
longer  axis,  than  the  projectile  of  smaller  diameter  and  the 
same  length. 

3.  If  we  have  two  similar  projectiles  of  different  densi- 
ties, the  dense  projectile  will  require  less  angular  velocity 
about  its  longer  axis,  since  its  mass,  and  hence  its  moment  of 
inertia,  is  greater.     Also,  a  shell  will  be  more  stable  and  re- 
quire less  angular  velocity  than  a  similar  shot  of  the'  same 
weight,  since  its  radius  of  gyration  is  greater. 

4.  Since  0  =  -j^-t  measures  the  deviation  of  the  longer 

IGO 
axis  in  the  time  /,  the  reciprocal,  —7,  may  be  taken   as  the 

measure  of  the  capacity  of  this  axis  to  resist  deviation  ;  and 
for  a  given  value  of  R  at  any  time  t  it  is  evident  that  by 

increasing  the  value  of  the  ratio  —  we  increase  the  stability 

of  the  projectile. 

VALUE  OF  R. — The  resistance  of  the  air,  R,  varies  with 
the  form,  cross-section,  and  velocity  of  the  projectile,  and 


296  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

with   the  density  of  the  air.     The  resistance  being  R,  the 
retardation  produced  by  this  resistance  will  be 


M* 

M  being  the  mass  of  the  projectile. 

This  value  of  the  retardation  has  been  determined  by 
experiment,  as  will  be  explained  in  Exterior  Ballistics. 

r> 

In  these  experiments,  the  expression  for  —  has  been  as- 
sumed to  be  (equations  (263)  and  (265),  Exterior  Ballistics) 


& 

in  which  A,    -„-,    and  c  are  constants,  whose  values  are  ex- 

plained  in  Exterior  Ballistics,  and  f  (v)  is  some  function  of 
the  velocity  of  the  projectile.     Hence  we  may  write 


For  a  given  value  of  v,  the  retardation  increases  with  the 

72 

factor  -=--   and  hence  this  factor  must  be  made  as  small  as 
W 

possible,  by  increasing  Wand  decreasing  d.    The  reciprocal 

W 
of  this  factor,  —  ,  may  then  be  taken  as  a  measure  of  the 

CL 

capacity  of  the  projectile  to  overcome  the  resistance  of  the 
air,  just  as  —  measures  its  stability. 

164.  Sectional  Density  —  How  it   May  be   Increased  —  Effect  of  its 
Increase  on  the  Gun. 

W 
SECTIONAL  DENSITY.—  The  factor  —  is  called  the  "  sec- 

tional  density"  of  the  projectile.     The  area  of  base  being 

W 

\7icF  ,  -  —  —  -  will  be  the  weight  of  the  projectiie  per  unit  area 


PROJECTILES  AND    ARMOR.  297 

W 

of  base,  and  hence  -^  is  taken  as  a  measure  of  this  weight, 

the  constant  factor  \n  being  omitted.  The  sectional  density 
is  very  important  in  considering  the  motion  of  a  projectile 
in  air,  and  also  in  the  gun. 

If  two  projectiles  have  the  same  initial  velocity,  but 
different  sectional  densities,  that  having  the  greater  sec- 
tional density  will  be  less  retarded  by  the  air,  equation  (244), 
and  consequently  will  lose  less  velocity.  Hence  for  a  given 
range,  its  time  of  flight  will  be  less,  and  being  exposed  to 
the  action  of  the  air,  and  other  deviating  causes,  for  a  less 
time,  its  accuracy  will  be  greater. 

If  the  two  projectiles  be  fired  with  the  same  angle  of 
elevation  and  the  same  initial  velocity,  that  having  the 
greater  sectional  density  will  have  the  greater  range,  since 
it  retains  more  velocity  at  the  end  of  each  successive  inter- 
val of  time. 

For  the  same  initial  velocity,  the  trajectory  or  path  of 
the  projectile  having  the  greater  sectional  density,  will  be 
flatter  or  less  curved  than  that  of  the  other,  because  since 
its  velocity  is  greater  at  any  point  of  its  path,  its  time  of 
passage  over  a  given  distance  is  less,  and  consequently  the 
time  during  which  the  force  of  gravity  acts  upon  it  to  pro- 
duce curvature  is  less.  This  gives  greater  accuracy  of  fire. 

An  increase  of  sectional  density  therefore  increases — 

1.  The  accuracy ; 

2.  The  range  ; 

3.  The  flatness  of  the  trajectory. 

How  IT  MAY  BE  INCREASED. — The  sectional  density 
may  be  increased  by  increasing  W  or  by  decreasing  d.  W 
may  be  increased  by  keeping  the  calibre  constant,  and  in- 
creasing the  length  of  the  projectile.  This  has  been  done 
with  modern  projectiles,  for  large  guns,  till  the  length  is  3! 
to  4  calibres. 

It  may  also  be  increased  by  increasing  the  density  of  the 
metal  of  which  the  projectile  is  made.  This  is  done  by 
using  lead  for  small-arm  projectiles,  but  this  material  does 
not  possess  sufficient  hardness  for  projectiles  for  larger 
guns. 


298  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  sectional  density  may  also  be  increased,  by  fixing- 
the  weight  W,  and  decreasing  the  calibre,  or  d.  This 
method  has  been  adopted  for  small  arms,  the  calibre  and 
weight  of  projectile  having  both  been  reduced  in  such  pro- 
portions as  to  increase  the  sectional  density. 

EFFECT  OF  INCREASE  OF  SECTIONAL  DENSITY  ON  THE 
GUN. — Let  P  represent  the  maximum  pressure  per  square 

inch  on  the  base  of  the  projectile  ; 
Mt  the  mass  of  the  projectile. 

Then  we  have 

M~  =  nr*P, (245) 

from  which 

dv        nr'P    _  nr*P        Pg 


dt    '       M  W  W 


.     (246) 


g 
Replacing  r  by  its  value  %d, 


(247) 


W  dv 

As  the  sectional  density  —  increases,  —  decreases,   and 

hence  to  obtain  an  increase  of  acceleration,  the  value  of  P, 
or  the  pressure  on  the  projectile,  and  consequently  that 
upon  the  gun,  must  increase.  Since  the  maximum  pressure 
is  fixed  by  the  strength  of  the  gun,  equation  (247)  limits  the 
value  of  the  sectional  density,  for  a  given  acceleration.  The 
initial  velocity  is 

(248) 


-=/: 


and  for  a  given  value  of  P,  this  velocity  will  decrease,  from 
equation  (247),  as  the  sectional  density  increases.  Hence 
when  rifled  guns  were  first  introduced,  using  the  old  quick 
powders,  the  pressures  could  not  be  increased,  and  conse- 
quently the  initial  velocities  of  the  projectiles  decreased. 
When  slow-burning  powders  were  adopted,  with  longer 


PROJECTILES  AND    ARMOR.  299 

bores,  the  sectional  density  of  projectiles  was  increased,  and 
also  the  initial  velocities,  with  less  maximum  strain  on  the 
gun.  The  reason  for  this  has  been  explained  in  Interior 
Ballistics. 

165.  Rifling — Kinds — Uniform — Increasing. 

RIFLING. — In  order  to  give  to  the  projectile  the  angular 
velocity  GO  required  in  equation  (242),  it  is  necessary  to  cut 
spiral  grooves  in  the  bore  of  the  gun,  and  to  attach  a  device 
to  the  projectile  which  will  fit  these  grooves.  The  spiral 
groove  in  the  gun  is  called  the  rifling. 

Let  v  denote  the  velocity  of  the  projectile  at  any  point 

of  the  bore ; 
0,  the    angle    made    by  the  tangent  to  one  of    the 

grooves,  with  an  element  of  the  bore  ; 
r,  the  radius  of  the  bore. 

The  velocity  of  the  projectile  along  the  groove,  is  the 
resultant  of  two  components,  v,  and  v  tan  0,  at  right  angles 
to  each  other. 

The  actual  velocity  of  rotation  of  a  point  on  the  surface 
of  the  projectile  is  cor,  and  this  is  equal  to  the  component 
v  tan  0.  Hence 

car  =  v  tan  0  ;     .*.  GO  = •  —  tan  0.   ...     (249) 

UNIFORM  RIFLING  OR  TWIST. — If  the  value  of  0  be 
constant  for  the  whole  length  of  the  bore,  the  rifling  or 
twist  is  said  to  be  uniform. 

In  this  case  the  angular  velocity  varies  directly  with  v 
and  inversely  with  r.  The  objection  to  uniform  rifling  is  as 
follows : 

When  the  projectile  starts  from  its  seat,  and  during  the 
first  part  of  its  path  in  the  bore,  the  pressure  of  the  powder- 
gas  rises  to  its  maximum,  and  the  gun  is  subjected  to  the 
greatest  stress  at  this  time. 

With  the  uniform  rifling,  the  angular  velocity  OD  is  im- 
pressed upon  the  projectile  at  this  time  also.  Hence,  while 
the  gun  is  subjected  to  its  greatest  stress,  due  to  the  start- 


I3OO  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

ing  of  the  projectile,  it  is  also  subjected  to  its  greatest  stress 
in  giving  rotation  to  the  projectile. 

After  rotation  is  once  acquired,  the  stress  due  to  this 
cause  falls  off  very  rapidly.  Therefore,  with  the  uniform 
twist,  both  these  stresses  act  together. 

INCREASING  TWIST. — If,  however,  the  angular  velocity  GO 
be  imparted  gradually  to  the  projectile,  it  moves  from  its 
seat  more  readily,  and  the  strain  on  the  gun  at  first  is  thus 
diminished.  When  the  powder  pressures  fall  off  along  the 
bore,  the  twist,  or  value  of  0,  gradually  increases,  till  it 
reaches  its  final  value  necessary  to  impart  the  angular 
velocity  GO  to  the  projectile.  In  this  case  the  stresses  are 
more  uniformly  distributed  along  the  bore,  and  the  gun 
strained  less  at  the  origin  of  motion,  while  the  final  velocity 
of  rotation  is  the  same. 

The  twist  in  this  case  is  called  an  increasing  twist,  as  the 
value  of  0  increases  gradually  from  the  breech.  In  modern 
guns  the  curve  ol  the  rifling,  when  developed  on  a  plane 
surface,  is  a  semi-cubic  parabola,  whose  equation  is 

ji  =  2pX. 

To  give  steadiness  of  rotation  to  the  projectile,  the  twist 
increases  from  the  breech  to  a  point  about  two  calibres 
from  the  muzzle,  and  from  this  point  to  the  muzzle  it  is 
uniform. 

166.  Twist  in  Terms  of  Calibre — Kinds  of  Grooves. 

TWIST  IN  CALIBRES. — The  twist  is  generally  expressed  in 
terms  of  the  calibre,  as  one  turn  in  ten  calibres,  etc. ;  mean- 
ing that  the  projectile  makes  one  complete  turn  in  passing 
over  a  length  of  bore  equal  to  ten  calibres,  etc.  Suppose 
the  groove  to  be  developed  (Fig.  163),  and  let  a  be  the  de- 
velopment of  one  turn  of  the  uniform  groove,  n  the  number 
of  calibres  in  which  the  projectile  makes  one  complete  turn, 
and  r  the  radius  of  the  projectile,  then  the  distance  AB 
=  2nr  and  BC  =  2nr,  and 

2TCT  71 

tan  0  —  -   -  =  — , 
n 


PROJECTILES  AND   ARMOR. 


301 


for  the  value  of  the  tangent  of  the  angle  of  the  rifling.     For 
the  increasing  groove,  0  is  variable,  but  for  any  point,  its 

value  is  — .     In  our  service,  the  rifling  of  sea-coast  guns  is 

increasing,  from  one  turn  in  50  calibres  at  the  breech,  to 
one  turn  in  25  calibres  at  a  distance  of  about  two  calibres 


from  the  muzzle.  For  the  field-guns,  the  rifling  was  for- 
merly uniform,  but  in  the  later  models  an  increasing  twist 
has  been  adopted. 

KINDS  OF  GROOVES. — The  number,  depth,  and  width  of 
grooves  depend  on  the  rotating  device.  By  a  groove  is 
understood  the  spiral  cut  made  in  the  bore,  and  by  a  land, 
the  space  between  two  adjacent  grooves. 

When  rifling  was  first  introduced,  the  grooves  were  few 
in  number,  and  as  the  points  of  contact  of  the  projectile 
with  the  bore  were  also  few,  these  points  required  consid- 
erable strength.  The  grooves  were  therefore  made  corre- 
spondingly deep  and  wide.  This  decreased  the  strength  of 
the  gun,  as  it  increased  the  diameter  of  the  bore  subjected 
to  the  action  of  the  powder-pressure.  With  a  change  in 
the  rotating  device,  the  grooves  increased  in  number,  and 
decreased  in  depth  and  width.  This  is  called  polygroove 
rifling,  and  adds  greatly  to  the  strength  of  the  gun.  In 
spite  of  this,  the  grooves  are  sources  of  weakness,  as  the 
action  of  the  powder-gas  tends  to  erode  them  at  the  junc- 
tion of  lands  and  grooves,  and  all  sharp  corners  must  be 
avoided. 

In  small  arms  the  presence  of  grooves  adds  to  the  diffi- 
culty of  cleaning  the  bore,  and  the  grooves  in  these  guns 
are  made  as  shallow  as  possible. 


3O2  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  shape  of  the  groove  in  the  sea-coast  guns  in  our  ser- 
vice is  shown  in  Fig.  164,  which  gives  the  grooves  of  the  8" 
rifle. 


FIG.  164. 

The  number  of  grooves  in  sea-coast  guns,  is  six  times  the 
calibre  of  the  gun  in  inches.     Thus  the  8-inch  rifle  has  48 
grooves  and  lands  ;  the  lo-inch,  60,  etc. 
167.  Rotating  Devices — Studded  System — Flanged  System. 

ROTATING  DEVICES. — The  spiral  grooves  having  been  cut 
in  the  bore  of  the  gun,  it  is  necessary  to  attach  some  device 
to  the  projectile  which  will  fit  into  these  grooves,  and  com- 
municate the  required  motion  of  rotation  to  it.  Although 
muzzle-loading  projectiles  are  practically  obsolete,  a  few 
such  guns  still  remain  in  our  service,  and  a  description  of 
the  means  employed  to  give  rotation  to  their  projectiles 
will  show  the  development  of  such  devices. 

Since  muzzle-loading  projectiles  are  of  less  diameter 
than  the  bore,  the  rotating  device  must  be  made  either  to 
fit  the  grooves  before  firing,  or  to  do  so  after  firing,  by  the 
action  of  the  powder-pressure.  Accordingly,  the  rotating 
devices  for  muzzle-loading  projectiles  are  divided  into  : 

1.  The  studded  or  flanged  system. 

2.  The  expanding  system. 

STUDDED  PROJECTILES. — This  system  was  generally  used 
for  muzzle-loading  projectiles  in  Europe,  and  especially  in 
England.  The  projectile  (Fig.  165)  was  provided  with  studs 
made  of  a  soft  metal,  such  as  zinc  or  copper,  to  avoid 
wearing  the  lands  of  the  rifling.  These  studs  were  arranged 
in  two  or  three  rows,  depending  on  the  length  of  the  pro- 
jectile, and  at  an  inclination  equal  to  the  angle  0  of  the 
grooves.  They  were  inserted  into  undercut  holes  in  the 
projectile,  and  subjected  to  pressure,  by  which  the  soft  metal 
was  forced  to  fill  the  holes.  (See  Fig.  165.) 


PROJECJ^ILES  AND    ARMOR. 


303 


The  advantage  of  this  system  is  that  the  projectiles  are 
certain  to  take  up  the  rifled  motion. 
The  disadvantages  are : 

1.  The    projectiles    must    be    adjusted    to 
each  particular  twist ;    and  if  two  guns  have 
the  same  calibre,  but  a  different  twist  of  rifling, 
different  projectiles  must  be  used  for  them. 

2.  They  cannot  be  used  with  an  increasing 
twist. 

3.  Owing  to  the   relatively  small  number 
of  studs,  the  pressure  upon  each  is  great,  and 
they  are  liable  to  shear.     To  avoid  this  they 
must   be   made  strong,   and    this    necessitates 
increased  depth  and  width  of  rifling  grooves, 
and  a  corresponding  weakening  of  the  gun. 

4.  The  stud-holes  in  the  projectile  weaken 


FIG.  165. 


the  latter,  and  their  irregular  surface  increases  the  resistance 
of  the  air  to  its  motion. 

5.  Unless  a  gas-check  is  provided  on  the  base  of  the  pro- 
jectile, the  escape  of  the  gas  between  the  projectile  and  the 
bore  erodes  the  latter. 

THE  FLANGED  SYSTEM. — In  this  system,  flanges  or  ribs, 
fitting  the  grooves,  were  used  instead  of  studs,  the  flanges 
being  made  generally  of  soft  metal,  except  in  case  of  the 
Whitworth.     The    principal    example    of   this  class   is    the 
Whitworth  projectile,  whose    cross-section    is   a 
hexagon,  and  whose  plane  faces  are  inclined  at  an 
angle  equal  to  that  of  the  rifling  (Fig.  166).     The 
bore  of  the  gun  is  rifled  to  correspond  (Fig.  i66a). 
In  this  case,  the  fit  of  the  pro- 
jectile in  the  bore  was  very  ac- 
curate,   and    any    slight   fouling 
interfered  with  the  loading.     As 
the  flanges  were  of  hard  metal, 
they  could  not  yield,  and  hence 
any  obstruction    was    liable    to 
FIG.  166.  FIG.  i66«.         burst   the    gun.     These    projec- 

tiles have  given  remarkable  results  as  regards  accuracy  and 
penetration,  but  they  are  no  longer  used. 


304  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY 

168.  Expanding  System — Hotchkiss. 

EXPANDING  SYSTEM. — This  system  has  been  largely  used 
in  the  United  States  for  muzzle-loading  projectiles. 

It  consists  in  placing  upon  the  rear  end  of  the  projectile, 
or  upon  its  cylindrical  body,  a  band  of  soft  metal,  such  as 
lead  or  brass,  which  is  expanded  by  the  action  of  the  pow- 
der-gas, and  forced  into  the  grooves  when  the  gun  is  fired. 

The  advantages  of  this  system  are  : 

1.  It  may  generally  be  used  with  either  a  uniform  or  an 
increasing  twist. 

2.  Projectiles  of  the  same  calibre,  having*  different  rotat- 
ing devices  of  this  class,  will  fit  any  gun  of  that  calibre,  and 
are  easily  loaded. 

3.  By  the  expansion  of  the  rotating  device  the  escape  of 
gas  between  the  projectile  and  bore  is  prevented,  since  the 
band  acts  as  a  gas-check. 

The  disadvantages  are: 

1.  In  some  of  the  devices  the  gas  was  uncertain  in  its  ac- 
tion, occasionally  failing  to  produce  expansion,  and  also  tear- 
ing off  the  rotating  device,  or  causing  it  to  "  strip  ;"  thus 
failing  to  give  the  rotary  motion  to  the  projectile,  and  when 
fired  over  the  heads  of  friendly  troops,  causing  accident  to 
them  from  the  fragments  of  the  band. 

2.  It  was  expensive,  and  required   careful   handling  to 
prevent  damage  to  the  rotating  device,  and  consequent  ina- 
bility to  load. 

3.  It  failed  to  centre  the  projectile  in  the  bore. 
The  principal  examples  of  this  class  are  : 

The  Hotchkiss ; 

The  Parrot t ; 

The  Eureka ; 

The  Butler. 

THE  HOTCHKISS. — This  projectile  consists 
(Fig.  167)  of  a  body,  a  ;  a  base,  b ;  and  a  jacket  of 
lead,  c,  of  the  same  diameter  as  the  body  of  the 
projectile. 

When  fired,  the  pressure  of  the  gas  forces  the 
base  b  up  on  a,  and  thus  the  lead  jacket  c  is  ex- 
panded into  the  grooves. 


PROJECTILES  AND   ARMOR. 


305 


169.  Expanding  System — Parrott— Eureka— Butler. 

PARROTT.— In  the  Parrott  system  a  brass  ring  or  band, 
a,  is  cast  upon  the  base  of  the  projectile 
(Fig.  1 68),  leaving  a  circular  channel 
or  groove,  b,  between  the  ring  and 
the  base.  The  gas  acting  in  the  chan- 
nel, forces  the  ring  outward  into  the 
grooves.  Frequently,  however,  the 
ring  was  torn  off  the  base  of  the  pro- 
jectile, as  its  hold  was  not  sufficient. 

EUREKA. — In  this  system  a  brass 
cup,  a  (Fig.  169),  is  placed  on  the  base 
of  the  projectile.  This  base  is  made 
in  the  form  of  a  frustum  of  a  cone, 
with  the  smaller  base  to  the  rear.  It 
has  several  longitudinal  grooves,  b,  cut 
in  it,  into  which  corresponding  projec- 


FIG.   168. 


tions  on  the  interior  of  the  cup  fit,  and 
these  prevent  the  rotation  of  the  cup 
around  the  axis  of  the  projectile,  so 
that  the  rotary  motion  communicated 
to  the  cup  by  the  rifling,  is  imparted 
to  the  projectile.  The  cup  is  curved 
where  it  rests  against  the  rear  end  of 
the  projectile,  and  to  prevent  stripping, 
it  is  held  in  place  by  the  screw-bolt  c. 
When  the  piece  is  fired,  the  gas-pressure 
forces  the  cup  forward  on  the  frustum 
of  the  base,  till  its  curved  surface  rests 
against  the  rear  of  the  projectile. 

This  causes  the  sides  of  the  cup 
to  expand  and  forces  them  into  the 
grooves.  It  is  a  very  satisfactory  muzzle-loading  rotating 
device,  and  is  still  in  use  in  our  service. 

BUTLER. — This  system  was  invented  by  Major  Butler  of 
the  Ordnance  Department,  and  consists  (Fig.  170)  of  a  brass 
ring  a,  having  a  lip  or  groove  b  in  it.  It  is  screwed  to  the 
base  of  the  projectile  to  prevent  stripping.  When  the  piece 
is  fired,  the  gas-pressure  acts  in  the  groove  b,  and  forces  the 


FIG. 


306 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


FIG.   170. 


outer  portion  c  of  the  ring  outward  into  the  grooves,  and 
the  inner  portion  d  against  the  base  of 
the  projectile,  thus  insuring  the  adher- 
ence of  the  ring  to  the  projectile.  It  is 
one  of  the  best  of  these  devices,  and  is 
still  in  service. 

170.  Breech-loading  Projectiles — First  Ro- 
tating Device — Hotchkiss  Projectile 
— Copper  Bands. 

ROTATING  DEVICES  FOR  BREECH- 
LOADING  PROJECTILES. — With  breech- 
loading  guns  the  powder-chamber  is 
larger  than  the  bore,  and  hence  the 
projectile  may  have  a  rotating  device 
larger  than  the  bore,  and  this  may  be 
compressed  into  the  grooves  by  the  action  of  the  powder- 
gas.  This  is  called  the  ''compression  system,"  to  distin- 
guish it  from  the  studded  or  flanged,  and  the  expansion 
systems.  Its  advantages  are  : 

1.  The  projectile  is  certain  to  take  the  grooves,  since  its 
rotating  device  is  compressed  into  them. 

2.  The  rotating  device  being  larger  than  the  bore  before 
firing,  it  acts  as  a  gas-check,  and  prevents  any  flow  of  gas 
between  the  projectile  and  the  bore. 

3.  It  may  be  so  shaped  as  to  fit  accurately  the  chamber 
of  the  gun  before  firing,  and  thus  perfectly  centre  the  pro- 
jectile, or  make  its   axis  coincide   with   that  of  the   bore. 
This  gives  increased  accuracy  of  fire,  and  it  is  impossible  to 
accomplish  it  with  any  muzzle-loading  system. 

Its  only  disadvantage  is  perhaps  a  slightly  greater  strain 
on  the  gun  due  to  the  increased  pressure  necessary  to  force 
the  band  into  the  grooves,  but  with  the  slow-burning  powder 
used  in  modern  guns  this  may  be  neglected.  In  fact  it  has 
been  shown  in  Interior  Ballistics  that  this  increased  resist- 
ance increases  the  muzzle  velocity. 

FIRST  ROTATING  DEVICE. — When  breech-loading  guns 
were  first  introduced,  the  rotating  device  was  a  jacket  of 
lead  (Fig.  171)  cast  on  the  body  of  the  projectile. 


PROJECTILES  AND   ARMOR. 


307 


The  objections  to  this  are  that  it  is  difficult  to  make  the 
lead  adhere  to  the  projectile,  and  it  becomes 
detached  in  flight.  This  is  dangerous  in  firing 
over  friendly  troops,  and  the  energy  commun- 
icated to  this  lead  jacket  is  lost ;  also  the  con- 
tact of  the  hot  metal  with  the  body  of  the  pro- 
jectile in  the  process  of  casting,  is  apt  to  injure 
the  structure  of  the  latter. 

One  rotating  device  of  this  class,  the  Hotch- 
kiss,  is  still  in  use  for  small-calibre  projectiles. 

HOTCHKISS  B.  L.  PROJECTILE.— The  body 
of  the  projectile  a,  Fig.  172,  is  grooved  cir- 
cumferentially  for  about  one  calibre  in  length, 

as  shown,  and 


1 

( 

( 

s 

••! 

o 

z 

a 

^ 

o: 

l_u 

C—  ( 

-6  ^ 

LJ 

cr 

( 

a  \ 

LJ 

0 

1- 

L_ 

^ 

La. 

LJ 
CD 

( 

< 

( 

| 

J 

1 

^ 

l-d' 


a 


FIG.  172. 

projections  d  of  the  band,  and  the  metal  thus 
displaced  is  forced  into  the  grooves  d'. 

COPPER  BANDS. — The  lead  jacket  was  next 
replaced  by  two  bands  of  copper,  Fig.  173, 
placed  at  equal  distances  from  the  centre 
of  gravity  of  the  projectile.  The  front  band 
a,  was  used  to  support  the  forward  por- 
tion of  the  projectile,  and  its  diameter  was 
slightly  less  than  that  of  the  bore  between 
lands.  The  rear  band  b,  was  of  a  larger 
diameter,  and  was  forced  into  the  grooves, 
giving  the  rotation. 


FIG.  171. 
over   these 
grooves  c,  is  placed  a  band 
of  brass,  b. 

Longitudinal  notches  are 
also  made  in  the  grooves  c, 
to  prevent  slipping  of  the 
band  around  the  axis  of  the 
projectile. 

When  the  gun  is  fired, 
the  gas  compresses  the  band 
into  the  grooves  on  the 
body  of  the  projectile,  and 
it  takes  a  corrugated  shape. 
The  lands  cut  through  the 


-a 


FIG.  173. 


308 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


171.  Rotating  Device  at  Present — Profile  of  Band — Placing  of  Band 
— Position  of  Band. 

RECENT  DEVICE. — It  was  found  that  the  front  bearing 
or  supporting  band  was  not  necessary,  and  in  modern  pro- 
jectiles it  is  replaced  by  a  slight  swell,  a,  Fig.  174,  at  the 
base  of  the  ogival  head.  The  surface  a  is  turned  to  a 
diameter  slightly  less  than  that  of  the  lands,  and  the  body 
of  the  projectile  left  as  it  comes  from  the  casting  or  forg- 
ing process. 

This  is  less  expensive,  and  leaves  the  metal  on  the  exte- 
rior, which  is  stronger  than  any  other  part  of  the  projectile. 

The  rotating  band  is  made  of  copper,  fitted  in  an  under- 
cut groove,  as  shown,  Fig.  174. 


a 


FIG.  174. 

DETAILS  OF  ROTATING  BAND. — In  modern  guns,  the 
powder-chamber  is  joined  to  the  bore  by  a  long  conical 
slope,  cd,  Fig.  174.  The  exterior  of  the  rotating  band  has 
a  slope  slightly  greater  than  this,  so  that  when  the  projec- 
tile is  in  place,  it  will  be  accurately  centred  by  the  rear 
portion  of  the  band,  and  this  part  of  the  band  will  also  act 
as  a  gas-check,  completely  closing  the  interior  of  the  bore. 
A  number  of  grooves  or  cannelures,  ^,  are  turned  on  the 
exterior  of  the  rotating  band,  to  diminish  the  amount  of 
metal  to  be  cut  through  by  the  lands,  allow  space  into  which 
the  portion  cut  out  may  be  forced,  and  at  the  same  time 
give  the  necessary  length  of  bearing  surface  on  the  lands, 
by  retaining  the  width  of  the  band  unchanged.  The  ex- 


PROJECTILES  AND    ARMOR. 


309 


terior  diameter  of  the  band  at  the  rear,  is  slightly  greater 
than  that  of  the  bore,  measured  from  the  bottom 
of  the  grooves. 

For  the  field  projectiles,  the  band  is  more  sim-  , 
pie,  being  a  plain  ring  of  copper  with  the  front 
and  rear  faces  bevelled,  Fig.  175. 

PLACING  THE  ROTATING  BANDS  IN  POSITION. 
— This  is  generally  done  in  our  service,  by  ham- 
mering the  band  into  place.     The  band  may  be 
made  in  two   semicircles,  or  in  a  single  piece  of    i 
copper,    whose   length   is   just    sufficient    to    en-     FlG-  J75- 

circle  the  projectile.  In  either  case 
the  cross-section  before  insertion  is 
as  in  Fig.  176  at  a. 

When  inserted  in  the  undercut 
groove  b  in  the  projectile,  it  is  ham- 
mered, or  subjected  to  pressure,  till 
it  takes  the  position  shown  at  e,  com. 
pletely  filling  the  groove. 

It  is  then  turned  in  the  lathe  to 
the  proper  dimensions. 

POSITION  OF  REAR  BAND. — The 
position  of  the  rotating  band  has 


'-d 


FIG.  176. 

great  influence  upon  the  range  and  accuracy  of  the  pro- 
jectile, as  has  been  shown  by  numerous  experiments.  It 
must  be  so  placed  that  the  distance  cd,  Fig.  176,  will  be 
sufficient  to  resist  the  shearing  effect  of  the  rifling,  which 
would  tend  to  strip  the  band  off  to  the  rear.  This  having 
been  provided  for,  the  best  position  of  the  band  is  deter- 
mined by  experiment. 

172.  Form  of  Projectiles — Head — Spherical  Density— Weight. 

FORM. — Numerous  experiments  have  been  made  to  de- 
termine the  form  of  projectile  that  will  best  overcome  the 
resistance  of  the  air. 

The  result  of  these  experiments  shows  that  the  resist- 
ance is  affected  by  the  shape  of  that  portion  of  the  head 
where  it  joins  the  cylindrical  body,  and  also  by  the  rear 
of  the  projectile,  since  the  shape  of  these  surfaces  affects 


3io 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


(See  "  Exterior  Bal- 


\ 


the  flow  of  the  air  along  its  sides, 
listics.") 

HEAD.  — The  heads  of  all 
modern  projectiles  are  ogival, 
the  radius  of  the  ogive  being 
from  2  to  3  calibres.  The  more 
pointed  form  gives  less  resist- 
ance, but  introduces  elements  of 
weakness,  and  hence  the  above 
radii  mark  the  limits  thus  far. 
The  head  is  described  with 
radii  as  shown  in  Fig.  177. 

SPHERICAL  DENSITY. —  Let 

W  be  the  weight  of  a  solid  spherical  projectile,  whose 
radius  is  r,  and  W  the  weight  of  the  oblong  projectile  of 
the  same  radius. 

The  ratio 

W 


FIG.  177. 


is  called  the  spherical  density  of  the  oblong  projectile,  and 
it  measures  the  number  of  times  the  weight  of  the  sphere 
is  contained  in  that  of  the  oblong  projectile.  We  have 

W  =  f  Trr'tf, 

in  which  d  is  the  weight  of  a  cubic  inch  of  the  metal  of  the 
projectile,  and  r  is  in  inches.  Making  d  =  £•  lb.,  which  is  its 
approximate  value,  and  taking  n  =  3,  we  have 

W  =  r* 


and  substituting  in  (250),  we  have 

r.         W 

^~    rs  ' 


(250 


which  is  generally  taken  as  the  measure  of  spherical  density. 

This  value  has  increased  from  2.0,  when  oblong  projec- 
tiles were  first  introduced,  to  3.0  in  1880,  and  4.7  in  1894. 

WEIGHT. — For  the  weight  of  a  spherical  projectile  we 
have 


PROJECTILES  AND    ARMOR. 


or  the  weight  of  a  spherical  projectile  in  pounds  is  equal  to 
the  cube  of  its  radius  in  inches. 

For  an  oblong  projectile  we  have,  equation  (251), 

W  =  S  X  r\ 

or  the  weight  of  an  oblong  projectile  in  pounds  is  equal  to 
its  spherical  density,  multiplied  by  the  cube  of  -the  radius 
in  inches.  Hence  having  the  date  of  manufacture  of  a  pro- 
jectile, its  spherical  density  is  known,  and  from  this  its 
weight.  This  rule  gives  very  close  approximations,  and 
avoids  the  necessity  of  remembering  anything  except  the 
spherical  density.  Since  the  weight  is  proportional  to  the 

W 
cube  of  the  calibre,  the  quotient  —  will  be  constant  for  all 

similar  projectiles. 

173.  Manufacture  of  Projectiles — Pattern — Flask — Molding— Gate 
and  Riser. 

PATTERN. — Cast-iron  projectiles  are  made  as  follows  : 

A  pattern  is  first  made  of  the 
shape  of  the  projectile  to  be  cast. 
Its  diameter  is  slightly  greater 
than  that  of  the  projectile,  to  I  '  '  r~6 

allow  for  the  shrinkage  or  con- 
traction of  the  metal  in  cooling. 
It  is  also  slightly  conical,  instead 
of  cylindrical,  on  the  exterior,  to 
permit  its  ready  withdrawal  from 
the  mold.  In  Fig.  178  the  pat- 
tern is  made  in  two  parts,  and 
each  part  is  conical  from  a  to  b. 
The  spindle  c  is  used  to  support 
the  pattern  in  molding,  and  to 
mark  the  position  of  the  core  in 
the  mold. 

It  terminates  in  a  conical 
bearing,  d.  FIG.  178. 

Core. — To  form  the  interior  cavity  in  a  cored  shot  or 
shell,  a  second  pattern  or  core  e,  Fig.  178,  is  required.    This 


-c 


312 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


core  is  made  of  a  mixture  of  sand  and  other  substances 
which  render  it  adhesive,  and  is  formed  upon  a  hollow 
spindle,  /,  which  terminates  in  a  conical  bearing,  g,  of  the 
same  size  as  d  on  the  shot-pattern  spindle.  The  spindle/ 
being  hollow,  and  having  holes  along  it,  allows  the  gases 
formed  by  the  contact  of  the  melted  metal  with  the  core,  to 
escape. 

FLASK. — The  pattern  for  the  shot  or  shell  is  placed  in  a 
box  called  a  flask,  Fig.   179.     This   flask  is   made  in  parts 


FIG.  179. 

corresponding  to  the  pattern  of  the  projectile,  and  these 
parts  are  bolted  together  before  casting.  It  contains  a 
cross-bar,  a,  at  the  top,  with  a  conical  hole  in  it,  into  which 
the  conical  bearing  of  the  spindle  fits  as  shown. 

MOLDING. — To  form  the  mold,  the  part  of  the  pattern 
containing  the  conical  spindle,  is  seated  in  the  cross-bar  a, 
and  this  part  of  the  flask,  with  pattern,  placed  on  a  board, 


PROJECTILES  AND    ARMOR.  313 

the  plane  xy  down.  Cylindrical  sticks  b  and  c  are  placed  as 
shown,  and  molding  composition,  composed  of  sand,  clay, 
and  carbonaceous  material,  rammed  in.  This  part  of  the 
flask  is  now  inverted,  the  remainder  of  the  pattern,  the 
flask,  and  the  cylindrical  stick  b  put  in  place,  and  molding 
composition  rammed  in  from  the  opposite  direction,  filling 
the  flask.  The  parts  of  the  flask  are  then  separated  along 
xy,  and  the  pattern  and  sticks  withdrawn. 

The  core,  having  been  separately  molded,  is  then  put  in 
place,  its  spindle  occupying  the  position  shown,  and  being 
centred  by  the  conical  bearing  in  the  cross-bar  a. 

The  parts  of  the  flask  are  next  bolted  together. 

GATE  AND  RISER. — The  channel  b  is  called  the  gate. 
The  metal  is  poured  through  it  into  the  mold.  In  large 
projectiles,  it  generally  enters  low  down,  and  in  a  tangen- 
tial direction,  to  give  a  rotary  motion  to  the  metal  as  it 
enters  the  mold,  and  thus  sweep  the  scoria  and  impurities 
to  the  centre  and  top. 

The  channel  c  is  called  the  riser.  It  allows  the  escape 
of  gas  from  the  mold,  and  the  collection  of  the  scoria,  and 
also  allows  fresh  metal  to.be  poured  in  to  fill  up  cavities  and 
make  up  for  shrinkage  due  to  cooling. 

174.  Operation  of  Casting — Kind  of  Iron  Used — Position  of  Head 
and  Base  of  Projectile  in  Mold — Steel  Projectiles. 

OPERATION  OF  CASTING. — The  cast  iron  is  melted  either 
in  cupola  or  reverberatory  furnaces,  and  run  into  ladles, 
from  which  it  is  poured  through  the  gate  b,  into  the  mold. 
The  pouring  is  continued  till  the  metal  fills  the  riser  c,  and 
fresh  portions  of  melted  metal  are  added  to  the  riser  as  the 
latter  sinks. 

As  soon  as  the  iron  has  cooled  sufficiently,  or  set,  the 
flask  is  removed,  the  core  broken  up,  the  spindle  drawn  out, 
and  the  projectile  covered  with  the  molding  composition,  to 
allow  it  to  cool  slowly.  If  a  chilled  projectile  is  to  be  cast, 
the  chill  is  inserted  in  the  mold  before  casting,  as  previously 
explained. 

KIND  OF  IRON. — For  small  projectiles,  since  they  cool 
rapidly,  and  become  very  hard,  soft  iron  is  employed.  For 


314  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

large  projectiles,  a  harder  and  tougher  iron  is  used.  The 
selection  of  the  proper  kinds  of  iron  can  only  be  determined 
by  experience,  and  it  is  usual  to  prescribe  a  certain  tensile 
strength  for  each  kind  of  projectile,  and  to  test  specimens 
from  a  number  of  them,  to  see  that  they  come  up  to  the  re- 
quired standard. 

POSITION  OF  HEAD  AND  BASE  IN  MOLD. — In  Fig.  179 
the  projectile  is  shown  cast  head  down,  with  the  core-spin- 
dle projecting  through  the  base.  This  position  gives  great 
density  to  the  head,  and  less  to  the  base.  For  armor- 
piercing  shot,  and  in  all  cases  where  great  strength  of  head 
is  required,  the  casting  is  made  in  this  position.  But  for 
shell,  especially  those  with  a  base  fuze,  it  is  important  to 
have  a  strong  and  sound  base,  as  if  it  is  weak  or  spongy ? 
the  gas  from  the  powder-charge  would  penetrate  the  base, 
and -burst  the  shell  in  the  gun.  In  this  case,  therefore,  the 
shell  would  be  cast  base  down. 

STEEL  PROJECTILES. — Forged  steel  projectiles  are  cast 
as  ingots,  and  are  forged,  and  bored  and  turned  to  proper 
dimensions. 

They  are  then  tempered  by  a  secret  process,  and  are  now 
made  of  such  hardness  and  toughness,  that  they  will  pene- 
trate the  best  armor-plates  whose  thickness  does  not  exceed 
\\  times  their  diameter,  without  cracking  or  deforming  the 
projectile. 

Cast-steel  projectiles  are  also  tempered  by  a  secret  pro- 
cess. 

175.  Inspection  and  Proof  of  Projectiles — Quality  of  Metal — Shape 

and  Dimensions — Eccentricity — Ballistic  Test. 
The  objects  of  inspection  are  : 

1.  To  test  the  quality  of  the  metal ; 

2.  To  see  that  the  shape  and  dimensions  agree  with  those 
specified  ; 

3.  To  see  that  the  centre  of  gravity  is  on  or  near  the 
longer  axis  of  the  projectile. 

QUALITY  OF  METAL. — This  is  determined  by  testing  spec- 
imens taken  from  different  lots.  For  cast-iron  projectiles, 
the  soundness  is  tested  by  striking  the  projectile  with  a  ham- 


PROJECTILES  AND   ARMOR.  315 

mer,  and  a  punch  is  used  to  determine  the  depth  of  any  holes 
that  may  be  discovered.  Finally  the  shot  or  shell  is  sub- 
jected to  water  or  steam  pressure,  applied  to  its  interior. 
Any  cracks  or  cavities  will  be  detected  by  the  escape  of 
the  water  or  steam.  Chilled  shot  are  struck  with  a  hammer, 
at  the  junction  of  head  and  body. 

For  Steel  S/wt  and  Shell  chemical  analyses  are  made,  to 
determine  the  composition.  After  the  final  treatment,  the 
shot  are  cooled  to  about  40°  F.,  and  then  suddenly  heated  by 
plunging  them  into  a  water-bath,  at  a  temperature  of  212°  F. 
When  they  become  uniformly  heated  to  this  temperature, 
they  are  suddenly  plunged,  with  their  axes  horizontal,  half 
way  into  a  bath  of  water,  at  a  temperature  of  40°  F.  Any 
great  initial  strain  to  which  they  may  have  been  subjected  in 
tempering,  will  be  detected  by  this  treatment.  The  shell 
are  subjected  to  an  interior  hydraulic  pressure  of  1000  Ibs. 
per  square  inch. 

SHAPE  AND  DIMENSIONS. — These  are  determined  by  tem- 
plets and  gauges.  For  example,  the  profile  of  the  projec- 
tile is  determined  by  using  a  templet  of  sheet  iron  or  steel, 
correctly  made,  and  applying  it  to  the  exterior  of  the  pro- 
jectile as  in  Fig.  180,  a  being  the  templet. 


FIG.  1 80.  FIG.  181. 

The  diameters  are  determined  by  two  rings,  called  ring 
gauges,  Fig.  181.  One  of  these  has  a  diameter  equal  to 
the  maximum  that  is  allowed,  and  the  other  the  mini- 
mum. 

The  maximum  ring  must  pass  overall  the  projectiles,  and 
'the  minimum  over  none. 

ECCENTRICITY. — When  the  centre  of  gravity  of  the  pro- 


TEXT-BOCK  OF  ORDNANCE  AND    GUNNERY. 


—a 


a 


jectile  does  not  lie  on  the  longer  axis,  the  projectile  is  ec- 
centric. 

This  eccentricity,  if  large,  affects  the 
flight  of  the  projectile,  causing  irregu- 
larity, and  hence  its  limits  must  not  ex- 
ceed a  certain  amount.  To  detect  it, 
the  projectiles  are  first  placed  on  a  roll- 
ing-table,  which  is  an  iron  table  having 
two  parallel  ribs,  a  a,  Figs.  182  and  183, 
at  a  distance  apart  slightly  less  than  the 
length  of  the  cylindrical  body  of  the  pro- 
jectile. 

This  table  being  leveled,  if  the  centre 
of  gravity  of  the  projectile,  does  not  CO- 
FIG.  182.  incide  with  the  longer  axis,  the  projec- 
tile when  rolled  on  the  ribs,  as  shown,  will  come  to  rest 
with  its  centre  of  gravity  below  that  axis.  If  no  eccen- 
tricity exists,  the  projectile  will  remain  indifferently 


D 


FIG.  183. 


in  any  position.  When  eccentricity  is  detected  by  this 
means,  its  amount  can  be  measured  with  the  eccentric  cali- 
pers. These  consist  of  a  curved  steel  arm,  d,  Fig.  183,  car- 


PROJECTILES  AND    ARMOR.  317 

rymg  a  sliding  point,  b,  and  a  scale,  c.  The  point  is  gradu- 
ated in  inches,  and  c  is  a  vernier  scale.  The  thickness  of 
wall  is  read  off  on  the  scale,  and  that  of  the  opposite  wall 
also.  One  half  the  difference  of  the  readings,  gives  the 
eccentricity. 

BALLISTIC  TEST. — Steel  shot  and  shell  are  subjected  to 
actual  firing  tests  against  armor-plates.  For  this  purpose  a 
certain  number  are  taken  from  each  lot  manufactured.  The 
shot  are  fired  with  a  striking  velocity  of  1625  feet-seconds 
against  a  steel  plate  i-J  times  the  calibre  of  the  gun  in  thick- 
ness, and  the  12"  mortar  shell  against  a  4^-inch  steel  plate, 
at  an  angle  of  60°.  The  shot  and  shell  must  penetrate  com- 
pletely in  each  case,  without  breaking  up. 

ARMOR. 

176.  Kinds  of  Armor. 

Armor  may  be  divided  into — 

1.  Chilled  cast  iron  ; 

2.  Compound ; 

3.  Steel. 

Wrought-iron  armor  is  now  obsolete. 

Chilled  Cast-iron  Armor. — This  armor,  on  account  of  its 
great  weight,  is  used  only  on  land,  in  the  form  of  turrets. 

It  is  manufactured  by  Gruson,  of  Germany,  and  is  cast 
in  large  blocks  of  the  proper  shape,  the  outer  face  of  the 
blocks  being  chilled,  and  thus  acquiring  great  hardness. 
These  blocks  are  built  into  turrets,  whose  form  is  shown  in 
the  text-book  of  the  Engineering  course.  It  depends  for  its 
great  resistance  upon  the  following : 

1.  Its  intense  surface  hardness  prevents  the  entrance  of 
the  projectile  ; 

2.  Its  great  mass  distributes  the  effect  of  the  blow ; 

3.  Its  curved  form  deflects  the  projectile. 

Its  resistance  to  penetration  is  greater  than  that  of  any 
other  armor. 

Compound  Armor. — Wrought-iron  armor  was  the  first  kind 
adopted,  and  it  had  sufficient  resistance  to  keep  out  the  or- 
dinary cast-iron  projectiles,  but  was  readily  penetrated  by 
those  of  chilled  cast  iron. 


3l8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

It  became  necessary,  therefore,  to  harden  the  face  ol  the 
armor  in  order  to  break  up  these  projectiles.  This  led  to 
the  introduction  of  the  compound  armor,  which  has  been 
extensively  used  in  England,  and  is  still  employed  there. 

It  is  formed  by  welding  a  hard  steel  face  to  a  wrought- 
iron  back,  and  the  armor  is  distinguished  into  two  makes, 
according  to  the  method  of  welding  adopted. 

The  two  methods  of  manufacture  are  : 

1.  Cammell  &  Co. —  Wilson  s  Patent. — The  firm  of  Cammell 
&  Co.  manufacture  compound  armor  by  the  Wilson  patent, 
which  consists  in  forming  a  back  of  wrought  iron,  by  forg- 
ing or  rolling.     This  back  is  placed  in  a  furnace,  raised  to  a 
welding    heat,  and  while  at  this   temperature  a   layer  of 
melted  steel  is  run  on  one  of  its  faces.     After  partially  cool- 
ing, the  compound  plate  is  removed  from  the  furnace  and 
passed  between  heavy  rolls,  to  reduce  it  to  the  proper  thick- 
ness, and  improve  its  quality.    The  steel  face  is  then  treated 
to  remove  strains. 

2.  Brown  &  Co. — Ellis  Patent. — This  method   consists  in 
forming  the  wrought-iron  back  and  hard  steel  face  sepa- 
rately.    These  are  then  placed  in  a  furnace  parallel  to  each 
other,  and  a  short  distance  apart,  and  raised  to  a  welding 
heat.     Melted  steel  is  then  run  between  the  plates,  welding 
them  together. 

177.  Steel  Armor — History — Improvements — Latest  Steel  Plates- 
Harvey  and  Tresidder  Processes  of  Surface  Hardening. 
HISTORY. — Steel  armor,  when  first  introduced,  was  hard 
and  brittle,  and  broke  up  under  the  action  of  projectiles. 
The  percentage  of  carbon  was  then  reduced,  and  the  plates 
no  longer  broke  up,  but  allowed  the  projectiles  to  penetrate. 
It  was  shown,  however,  by  the  Italian  experiments  at  Spez- 
zia  in  1876,  that  the  low  steel  plate  was  superior  to  those 
made  of  wrought  iron.  To  prevent  the  penetration  of  pro- 
jectiles, the  face  of  the  plate  was  tempered  in  oil,  or  oil- 
hardened,  and  the  plate  then  annealed,  to  remove  internal 
strains.  As  projectiles  improved,  however,  this  hardness 
was  not  great  enough  to  resist  penetration,  and  hence  new 
improvements  were  made. 


PROJECTILES  AND    ARMOR.  319 

IMPROVEMENTS. — These  consist  generally — 

1.  In  having  better  facilities  for  the   mechanical  treat- 
ment  of  steel  in  large    masses,  such    as    heavy    hammers, 
forging-presses,  etc. 

2.  Combination  of  the  steel  with  other  ingredients,  such 
as  nickel,  which  increases  its  toughness  and  tenacity,  and 
consequently  decreases  its  tendency  to  break  up. 

3.  Special  treatment  of  the  steel,  as  the  Harvey  process, 
by  which  the  face  is  made  hard,  while  the  back  retains  its 
toughness. 

LATEST  STEEL  PLATES. — From  the  time  of  the  Italian 
experiments  in  1876,  up  to  those  at  Annapolis  in  1890,  com- 
petitive trials  have  been  going  on  between  the  steel  and  the 
compound  armor. 

The  tests  at  the  latter  place,  showed  the  superiority  of 
the  all-steel  plate,  and  it  has  been  adopted  in  our  Navy. 

The  steel  plates  which  have  given  the  best  results  up  to 
the  present  time,  are  known  as  high-carbon  nickeled  steel 
and  low-carbon  nickeled  steel,  referring  to  the  relative  quan- 
tity of  carbon  in  the  alloy,  although  it  is  small  in  each  case. 
The  high-carbon  nickeled-steel  plate  has  so  far  given  the  best 
results.  All  the  plates  are  hardened  on  the  surface  by  the 
Harvey  process. 

HARVEY  PROCESS. — This  consists  in  carbonizing  to  a 
higher  degree  the  outer  surface  of  the  plate,  for  a  certain 
depth,  depending  on  the  dimensions  of  the  plate,  and  then 
hardening  this  surface. 

The  process  is  as  follows :  The  plate  is  embedded  in 
sand  and  clay  in  a  furnace,  leaving  a  certain  thickness  ex- 
posed. The  furnace  is  then  filled  with  carbonaceous  material, 
well  packed  over  the  exposed  portion  of  the  plate,  and  the 
whole  raised  to  a  high  temperature,  which  is  maintained  for 
some  time.  The  material  is  then  removed,  and  when  the 
plate  has  cooled  sufficiently,  its  surface  is  hardened  by  the 
application  of  cold  water. 

TRESIDDER  PROCESS. — This  process  is  used  in  England, 
and  consists  in  heating  the  plate  to  a  certain  temperature, 
and  applying  cold  water  to  the  surface  under  heavy  press- 
ure, and  through  a  number  of  small  holes,  thus  producing 


320  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

numerous  small  streams  of  water  acting  together.  The  idea 
is  that  the  force  with  which  the  water  is  applied,  brings  it 
directly  into  contact  with  the  hot  metal,  thus  cooling  it 
rapidly,  and  preventing  the  formation  of  the  envelope  of 
steam  (spheroidal  state)  around  the  particles  of  water,  and 
the  consequent  slow  rate  of  cooling,  which  would  be  the 
case  if  the  water  were  applied  without  pressure. 

178.  Effect  of   Projectiles  on  Armor  —  Early  Armor  —  Compound 

Armor — Steel  Armor. 
Armor  yields  in  two  ways  : 

1.  By  racking,  or  breaking  up ; 

2.  By  punching. 

EARLY  ARMOR — Punching. — Wrought-iron  armor  was  at 
first  generally  attacked  by  heavy  projectiles,  moving  with 
low  velocities,  as  with  the  old  1 5-inch  smooth-bore.  Al- 
though the  armor  itself  was  soft,  and  yielded  naturally  by 
punching,  the  effect  of  these  projectiles  was  to  break  its 
fastenings,  and  cause  it  to  rack.  As  guns  and  projectiles  in- 
creased in  power,  however,  this  armor  yielded  entirely  by 
punching.  That  is,  the  effect  of  the  blow  was  to  punch  a 
hole  through  the  armor,  and  if  the  bolts  held,  no  part  of 
the  plate  beyond  that  struck,  was  affected. 

Racking. — The  object  of  armor,  however,  being  to  keep 
out  projectiles,  this  defect  led  to  the  introduction  of  the 
harder  kinds,  as  shown.  This  hard  armor,  instead  of  yield- 
ing locally  to  the  blow  of  the  projectile,  distributed  the 
energy  of  that  blow  over  a  greater  mass  of  the  plate,  and 
when  the  energy  was  sufficient,  the  plate  broke  up,  or  was 
racked. 

COMPOUND  ARMOR.— The  effect  of  projectiles  upon  this 
armor,  is  to  break  up  the  hard  steel  face,  and  to  punch  the 
wrought-iron  back.  The  punching  effect  is,  however,  very 
much  diminished  by  the  energy  lost  in  breaking  up  the 
steel  face.  The  difficulty  with  this  armor  seems  to  be  that 
the  welding  of  the  steel  face  to  the  wrought-iron  back  is 
uncertain,  and  hence  after  a  few  blows,  the  steel  face  breaks 
up,  and  separates  from  the  wrought-iron  back.  Also  the 
face  being  elastic,  and  the  back  having  no  elasticity,  the 


PROJECTILES  AND    ARMOR.  321 

former,  after  being  struck,  tends  to  recover  its  first  position, 
while  the  latter  does  not.  This  increases  the  tendency  of 
the  front  and  back  to  separate.  It  follows  that  a  compound 
plate  must  have  a  rigid  support  in  rear  for  the  best  results. 

STEEL  ARMOR. — This  armor  at  first  yielded  by  rack- 
ing, owing  to  its  hardness  and  brittleness.  Oil-hardening, 
however,  decreased  its  brittleness  and  increased  its  tough- 
ness, so  that  the  effect  of  the  improved  projectile  was  to 
punch  it. 

The  modern  processes  of  surface-hardening,  however, 
have  combined  hardness  with  toughness,  so  that,  at  the  pres- 
ent day,  the  armor  resists  both  racking  and  punching  to  a 
remarkable  degree.  The  history  of  the  improvement  is  ob- 
vious :  decrease  of  hardness  and  brittleness  to  decrease 
racking,  and  afterwards  a  combination  of  hardness  and 
toughness  to  prevent  both  punching  and  racking. 

179.  Backing — Fastenings  for  Old  Armor. 

BACKING. — That  portion  of  an  armored  structure  di- 
rectly in  rear  of  the  plate,  is  called  the  backing,  and  the 
character  of  this  backing  depends  upon  that  of  the  armor. 

Chilled  Cast  Iron. — This  armor  has  no  backing,  or  rather 
the  cast  iron  itself  may  be  regarded  as  forming  the  backing 
for  the  hard  chilled  face,  since  the  thickness  and  mass  are 
great. 

Compound  Armor. — For  this  armor,  a  rigid  backing  is  re- 
quired, to  give  the  best  results.  For  land  structures,  a  rigid 
backing  may  be  used,  since  weight  is  no  objection,  but  for 
ships,  such  a  backing  is  impossible,  and  it  would  therefore 
seem  that  this  armor  cannot  give  the  best  results  when  used 
under  such  circumstances.  It  is,  however,  the  standard 
armor  of  the  British  Navy.  An  objection  to  the  rigid  back- 
ing is  that  it  tends  to  cause  racking  of  the  armor-bolts. 
When  an  elastic  backing  is  used  with  this  armor,  it  allows 
the  plate  as  a  whole  to  yield  to  the  blow  of  the  projectile. 
But,  as  before  stated,  the  steel  face,  being  elastic,  returns  to 
its  former  position  after  the  blow,  while  the  wrought-iron 
back  does  not,  and  hence  there  is  a  tendency  for  the  face 
and  back  to  separate.  The  rigid  backing,  on  the  other  hand, 
has  the  opposite  effect. 


322 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


Steel  Armor. — This  armor,  being  elastic,  requires  an  elastic 
backing,  and  not  a  rigid  one,  since  the  elastic  backing  allows 
the  plate  to  yield  to  the  force  of  the  blow,  and  the  elasticity 
of  the  plate  causes  it  to  return  to  its  former  position. 

Fig.  184  shows  the  arrange- 
ment of  backing  as  generally 
used,  and  may  consist  of  one  or 
two  thicknesses  of  timber,  by 
placed  against  the  steel  sides, 
a  a,  of  the  vessel. 

FASTENINGS  FOR  OLD  AR- 
MOR.— The  original  armor-bolt 


FIG.  185. 


FIG.  184. 


FIG.  186. 


for  wrought-iron  armor,  was  shaped  as  shown  in  Fig.  185. 

The  objections  to  this  bolt  were  : 

I.  If  under  water,  it  leaked. 

*  2.  When  the  plate  was  struck,  the  bolt  would  snap  at 
the  bottom  screw-thread  a,  and  the  nut  would  fly  off,  acting 
as  a  projectile. 

The  French  made  the  first  attempt  to  remedy  this,  by 
using  an  ordinary  wood-screw,  Fig.  186,  which  screwed  into 
the  backing,  but  did  not  pass  completely  through  it.  This 
prevented  leakage,  and  the  flying  of  the  bolt-heads  about 
the  deck. 

The  English  changed  the  arrangement  of  the  armor-bolt 


PROJECTILES  AND    ARMOR. 


323 


by  placing  a  rubber  washer,  k,  under  the  nut,  and  cutting  a 
plus  thread  on  the  bolt,  as  in  Fig.  187.     In  this  case  the  bolt 


FIG.  187. 

has  the  same  strength  throughout,  the  thread  is  not  a  source 
of  weakness,  and  the  rubber  washer  allows  a  certain  play  in 
the  direction  of  the  length,  and  thus  prevents  snapping  from 
the  sudden  strain,  and  it  also  prevents  leaking. 

180.  Improved   Fastenings  for  Iron  Armor  —  For  Steel  Armor — 

Tests  of  Armor-plates. 

IRON  ARMOR. — In  addition  to  the  strains  brought  to  bear 
upon  the  bolt  in  the  direction  of  its  length,  causing  elonga- 
tion   and    snapping     in     the    older 
forms,  there  is  a  cross-strain  due  to 
the  displacement  of  the  armor  side- 
ways.    To  obviate  this,  the  English 
spherical-headed  bolt  was    devised, 
as  shown  in  Fig.  188.    This  shape  of 
FIG.  188.  head  and  nut,  causes  the  strain  to  be 

always  along  the  axis  of  the  bolt ;  and  to  allow  the  bolt  to 
take  its  normal  position  when  the  plate  is  displaced  laterally, 
a  clearance  is  made  around  it. 

STEEL  ARMOR. — With  this  armor,  or  with  the  compound 
armor,  where  it  is  necessary  to  preserve  the  steel  or  hard- 
ened face  intact,  the  bolt  must  not  pass  through  the  plate. 
It  is  therefore  screwed  for  a  short  distance  into  the  back  of 
the  plate.  In  naval  vessels,  the  backing  is  comparatively 
thin,  and  hence  the  bolt  must  be  lengthened  by  some 
means,  so  that  the  stretch  per  unit  of  length  may  not  be 
sufficient  to  break  the  bolt.  The  following  arrangement  is 
adopted  in  the  Navy  (Fig.  189). 


324 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


a  is  the  armor-plate;  b,  the  backing;  c,  the  armor- 
bolt,  reduced  in  diameter  as  shown,  to  give  lateral  play 
in  the  iron  pipe  d,  which  passes  through  the  backing 
and  furnishes  a  seat  for  the  bolt ;  e  and  /,  rubber  wash- 
ers which  are  set  up  by  the  pressure  of  the  nut  g,  and 
prevent  leaking  ;  h,  a  sleeve,  whose  object  is  to  increase  the 
length  of  the  bolt,  so  that  the  elongation  per  unit  length 


FIG.  189. 

when  the  plate  is  struck,  may  prevent  fracture ;  /,  a  cup- 
shaped  washer,  containing  the  rubber  washer  k,  and  the 
iron  washer  /.  The  washer  k  gives  elasticity  to  the  whole 
system.  The  sleeve  h  distributes  the  pressure  of  the  nut  g 
over  a  large  area  of  the  sides  of  the  ship,  and  also,  as  stated, 
increases  the  length  of  the  bolt.  The  number  of  bolts  is 
greater  for  the  steel  and  compound  armor,  than  for  the  old 
wrought-iron  armor. 

TESTS  OF  ARMOR-PLATES. — The  test  of  armor-plate  pre- 
scribed by  the  Ordnance  Department  is  as  follows  :  One 
plate  is  selected  from  a  lot,  and  is  bolted  to  an  oak  backing 
36  inches  thick,  properly  supported,  with  rubber  washers 
placed  between  the  steel  washers  of  the  bolts  in  rear.  The 
calibre  of  the  gun  is  to  that  of  the  plate  as  i  :  i-J;  .that  is, 
for  a  Q-inch  plate  an  8-inch  gun,  etc.  One  armor-piercing 
shot  is  fired  from  this  gun,  so  that  the  centre  of  the  shot-hole 
shall  not  be  nearer  any  edge  of  the  plate  than  2\  calibres. 

The  projectile  must  have  the  following  striking-energy : 

For  an  8-inch  gun 3000  foot-tons 

For  a  lo-inch  gun 5000        " 

For  a  1 2-inch  gun 7643         " 


PROJECTILES  AND    ARMOR.  $2$ 

Under  these  conditions,  the  whole  of  the  projectile  must 
not  get  through  the  plate,  nor  must  the  plate  break  up,  or 
pieces  be  detached,  or  cracks  produced  which  expose  the 
backing  to  view. 

181.  Penetration  of  Armor  —  Wrought  Iron  —  Steel. 

WROUGHT  IRON.  —  Most  of  the  formulas  for  penetration 
have  been  deduced  for  wrought-iron  armor,  on  account  of 
the  length  of  time  it  has  been  in  use,  and  the  numerous  ex- 
periments that  have  been  made  upon  it. 

In  deducing  these  formulas  two  different  hypotheses 
have  been  adopted  : 

1.  That  the  projectile  acted  as  a  punch,  separating  a 
disk  of  metal  from  the  plate.     In  this  case,  the  resistance  to 
be  overcome,  was  the  resistance  of  the  metal  to  shearing 
along  the  circumference  of  this  disk,  and  hence  the  energy 
of  the  projectile  to  overcome  this  resistance  was  estimated 
per  inch  of  shot's  circumference,  and  was  obtained  by  di- 

E 

viding  the  total  energy  by  the  circumference,  or  —  . 

Ttd 

2.  That  the  projectile  acted  as  a  wedge,  forcing  the  par- 
ticles of  the  metal  apart.     In  this  case  the  penetration  is 
proportional  to  the  energy  per  unit  of  area  of  cross-section, 

E 

or  —  - 
nr* 

The  principal  formulas  deduced  under  the  first  hypothe- 

esis  are  : 

/3  =  JL  ;  (Fairbairn's)     .     .     .     (252) 

Ttdk 

/2.035  =  —  —  .  (English  Admiralty)     (253) 


(Muggiano)      .     .     .     (254) 


And  under  the  second  hypothesis  : 


5575 


(deMarre's)    .    .     .     (255) 


326  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

0'14*'1  (Maitland>s)    •  •   • 

(Krupp>s)  •  •  •  •  (257) 

(G*vre)  .....  <258) 


In  these  formulas 

/  is  the  thickness  of  wrought  iron,  in  inches,  which 

the  projectile  will  penetrate  ; 
E,  the  energy  of  the  projectile  in  foot-tons  ; 
d,  its  diameter  in  inches  ; 
/,  its  weight  in  pounds  ; 
v,  its  striking  velocity  in  feet-seconds  ; 
£,  a  constant. 

STEEL  ARMOR.  —  For  steel  armor,  it  was  customary  to 
calculate  the  penetration  in  a  wrought-iron  plate  of  the 
same  thickness,  and  add  a  certain  percentage  of  increase  of 
resistance,  varying  from  10  to  30  per  cent.  This  method  is 
not  satisfactory,  as  steel  armor  varies  greatly  in  resistance 
according  to  treatment  ;  and  for  the  modern  Harveyized 
plates,  penetration  seldom  occurs,  owing  to  the  hard  face, 
unless  the  gun  greatly  overmatches  the  plate. 

The  formulas  generally  used  are  those  of  de  Marre,  as, 
follows  : 

For  soft  plates  of  Creusot  steel,  backed, 

r-7  =  0.0009787^  ......    (259) 

For  the  steel  plates  used  as  protection  against  steel  shell 
from  rapid-fire  guns,  unbacked, 

f>->  =  0.000734^.  .     .....     (260) 

For  the  wood  backing,  with  plate  in  front  of  it, 

/•••  =  0.006168^-  .......     (261), 


PROJECTILES  AND    ARMOR.  $2? 

Captain  Orde  Browne  gives  a  rule  which  enables  some 
idea  to  be  formed  of  the  relative  powers  of  guns  against 
armor,  as  follows  :  The  penetration  of  a  projectile  in  wrought- 
iron  armor  is  one  calibre  for  every  thousand  feet  striking  vel- 
ocity. 

For  example,  a  lo-inch  projectile,  striking  with  a  velocity 
of  1200  feet-seconds,  will  penetrate  1.2  calibres,  or  12  inches. 


CHAPTER  V. 
FUZES  AND   PRIMERS. 

FUZES. 

182.  Definition— Classification— Time  Fuzes— Requisites— Dif&cul- 
ties. 

DEFINITION. — Fuzes  are  the  means  used  to  ignite  the 
bursting  charge  of  a  projectile  at  any  point  of  its  flight,  or 
upon  impact. 

CLASSIFICATION. — They  are  classified  according  to  their 
mode  of  action,  into— 

1.  Time; 

2.  Percussion ; 

3.  Combination ; 

4.  Delayed  action  fuzes. 

TIME  FUZES. — A  time  fuze  is  one  which  ignites  the  burst- 
ing charge  at  some  fixed  time  after  the  projectile  has  left 
the  muzzle,  and  it  consists  generally  of  a  column  of  compo- 
sition, whose  rate  of  burning  is  known,  which  is  set  on  fire 
by  the  discharge  of  the  piece,  and  whose  time  of  burning  is 
regulated  by  the  length  of  the  column. 

REQUISITES. — The  requisites  of  a  good  time  fuze  are  : 

1.  Its  rate  of  burning  should  be  uniform,  and  not  affected 
by  storage  or  changes  of  climate. 

2.  It  must  be  safe  in  handling,  and  certain  in  its  operation. 
These  conditions  are  very  difficult  to  fulfil,  and  hence  a 

good  time  fuze  is  perhaps  the  most  difficult  one  to  obtain. 

Recent  improvements  have,  however,  done  much  to 
obviate  the  difficulties  formerly  experienced. 

DIFFICULTIES. — The  difficulties  in  making  a  reliable 
time  fuze  are : 

328 


FUZES  AND   PRIMERS.  329 

1.  To  obtain  a  column  of  composition  whose  rate  of  burn- 
ing is  uniform. 

The  rate  of  burning  of  a  composition  depends  upon  its 
density,  trituration,  composition,  and  degree  of  moisture,  as 
explained  in  Interior  Ballistics.  For  the  same  composition, 
it  is  very  difficult  to  obtain  a  uniform  density  throughout  a 
long  column.  The  old  method  of  preparing  a  time-fuze  was 
to  place  a  small  quantity  of  the  composition  in  the  fuze-case, 
and  strike  it  a  certain  number  of  blows  with  a  mallet  and 
drift,  and  repeat  this  operation  till  the  fuze  was  completed. 
This  did  not  give  uniform  density. 

A  second  method  was  to  subject  it  to  hydraulic  pressure, 
but  this  also  failed.  The  method  now  in  use  gives  better 
results,  and  will  be  explained. 

2.  For  long  times  of  burning,  a  long  column  of  composi- 
tion is  required,  and  the  results  obtained  by  the  old  method 
were  so  unsatisfactory,  that  the  ingredients  of  the  composi- 
tion were  varied,  in  order  to  give  a  decreased  rate  of  burn- 
ing and  thus  shorten  the  column.     This  changed  irregularly 
the  rate  of  burning,- increased  the  difficulty  of  preservation, 
and  also  increased  the  residue. 

3.  It  was  found  impossible  to  guard  against  the  changes 
due   to   storage,   climate,   etc.,  as  they   affected   both   the 
composition,  and  the  fuze-case. 

4.  After  a  uniform  rate  of  burning  is  obtained,  the  press- 
ure  of  the  air  on  the  composition,  during  flight,  changes 
this  rate. 

5.  With   modern   breech-loading  guns,  and  high  veloci. 
ties,  a  small  error  in  burning,  increases  the  error  in  burst- 
ing  of  the  projectile. 

6.  The  flame  from   the  powder-charge  will  no  longer 
ignite  the  fuze. 

183.  Time  Fuzes— Difficulties,  How  Overcome. 

To  overcome  these  difficulties,  the  following  changes  in 
manufacture  have  been  made : 

Uniform  Rate  of  Burning. — To  obtain  a  uniform  rate  of 
burning,  and  a  column  of  composition  of  sufficient  length  to 
answer  for  the  greatly  increased  ranges,  a  lead  tube  0.62 


330  TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 

inch  in  diameter  is  filled  with  mealed  powder.  The  ends 
are  then  closed,  and  the  tube,  with  the  enclosed  powder, 
drawn  out  by  a  process  similar  to  that  of  wire-drawing-,  till 
the  diameter  is  decreased  to  0.152  inch.  The  rate  of 
burning  is  tested  by  burning  inch  lengths  of  this  compressed 
powder,  and  its  rate  is  found  to  be  very  uniform.  In  this 
case,  the  pressure  is  applied  in  the  direction  of  the  shortest 
dimension  of  the  column,  so  that  it  is  more  uniform  in  its 
effect ;  and  if  there  be  any  difference  in  density,  this  differ- 
ence, is  neutralized  by  the  burning  of  the  column  at  right 
angles  to  the  direction  of  the  pressure,  so  that  the  same 
variation  of  density  exists  throughout  each  cross-section. 

Changes  of  Climate,  etc. — These  have  less  effect  upon  the 
composition,  because  it  is  contained  in  a  metallic  case  which 
is  less  subject  to  change. 

Variation  due  to  Pressure  of  Air  in  Flight. — This  is  cor- 
rected for,  as  far  as  possible,  by  graduating  the  fuze  tempo- 
rarily with  the  rate  of  burning  as  determined  at  rest,  and 
then  correcting  this  graduation,  by  actual  test,  on  the  firing- 
ground. 

Ignition  of  Fuze. — With  the  old  fuzes,  and  muzzle-loading 
projectiles,  there  was  always  a  space  between  the  surface  of 
the  bore  and  that  of  the  projectile,  through  which  the  flame 
from  the  powder-charge  could  pass  to  ignite  the  fuze.  This 
was  called  the  "  windage."  With  modern  breech-loading 
projectiles,  this  space  is  closed  by  the  band  of  the  projectile, 
and  hence  the  flame  cannot  pass  through  to  ignite  the  fuze. 
The  arrangement  for  accomplishing  this  with  the  modern 
time  fuze,  will  be  explained. 

184.  Older  Forms  of  Time  Fuze  in  Use— Mortar  Fuze— Sea-coast 

Fuze— Bormann  Fuze. 

The  older  forms  of  time  fuze  still  in  use  in  the  U.  S. 
service  are : 

The  mortar-fuze ; 
The  sea-coast  fuze ; 
The  Bormann  fuze. 

MORTAR  FUZE. — This  is  used  in  the  old  siep-e  and  sea- 


FUZES  AND    PRIMERS. 


33* 


coast  smooth-bore  mortars.     It  consists  (Fig.  190)  of  a  coni- 
cal case  or  plug,  a,  of  wood  graduated  on 
the  exterior  into  inches  and  tenths.     On  the  c'{ 
interior  there  is  a  cylindrical  cavity,  b,  bored 
out  nearly  to  the  bottom,  and  filled  with  the 
fuze-composition,  driven  as  explained.     The 
top  of  this  cavity  is  enlarged  at  c,  and  filled 
with  mealed  powder  moistened  with  alcohol, 
to   insure   ignition   from    the  flame   of   the 
powder-charge.      This   is   covered    with   a 
paper  cap,  cfj  on  which  is  marked  the  rate 
of  burning  in  seconds  per  inch.     The  gradu- 
ations begin  at  d,  and  stop  at  e.     To  prepare 
this  fuze  for  use,  the  paper  cap  is  removed, 
the  fuze  cut  at  the  proper  division,  counting 
from  the  top,  by  sawing  off  the  lower  end,  or 
better  by  boring  a  hole  into  the  composition 
with  a  gimlet,  as  at/,  as  this  prevents  the  composition  from 
being  dislodged  by  the  shock  of  discharge,  and  finally  by 
driving  with  a  drift  the  fuze  into  the  fuze-hole  of  the  shell. 

THE  SEA-COAST  FUZE. — This  was  used  in  the  old  smooth- 
bore guns,  and  at  present  in  the  1 5-inch  Rodman  gun. 

For  ordinary  firing,  this  fuze  (Fig.  191)  is  composed  of  a 


FIG.  191. 


conical  wood  plug,  a,  with  a  conical  hole,  b.     In  this  hole  is 
placed  the  fuze,  c,  which  is  contained  in  a  conical  paper  case. 


332 


TEXT- BOOK  OF  ORDNANCE  AND    GUNNERY. 


The  fuzes  are  of  variable  composition,  and  are  marked  on 
the  exterior  according  to  their  time  of  burning.  For  ricochet 
firing  over  water,  and  for  heavy  charges,  a  brass  fuze-plug, 
d,  of  the  same  shape  is  used,  the  distinctive  feature  being 
the  water-cap,  e,  which  is  a  brass  cap,  having  a  zigzag  chan- 
nel, filled  with  mealed  powder.  The  shape  of  this  channel 
renders  the  access  of  water  difficult,  and  hence  prevents  the 
extinction  of  the  composition. 

THE  BORMANN  FUZE. — This  was  used  with  spherical 
shell  and  shrapnel,  in  the  field  service. 

It  consists  (Fig.  192)  of  a  pewter  fuze-case,  a,  containing 
a  ring  of  composition,  b.  Over  this  ring,  b,  lies  an  arc,  c, 
graduated  in  seconds.  At  the  zero  end  of  the  arc,  this  ring, 


FIG.  192. 


by  communicates  with  a  channel,  d,  filled  with  fine  powder, 
leading  into  a  chamber,  e,  filled  with  the  same  powder, 
which  is  supported  by  a  tin  disk,  /.  The  composition,  b,  is 
pressed  into  its  recess  in  the  direction  of  its  shortest  dimen- 
sion, and  burns  around  the  ring  at  right  angles  to  this  direc- 
tion. Hence  the  fuze  possesses  one  of  the  good  qualities  of 
the  modern  time-fuze.  The  other  end  of  the  ring  of  com- 
position, has  no  communication  with  the  chamber  e.  Owing 
to  its  shape,  and  the  material  of  which  the  case  is  made,  this 
fuze  is  liable  to  be  driven  into  the  shell  by  the  shock  of  dis- 
charge ;  and  to  prevent  this,  and  increase  the  effect  of  the 
bursting-charge  in  the  projectile,  a  wrought-iron  disk,  g,  is 
screwed  into  the  fuze-hole,  below  the  fuze. 

The  action  of  the  fuze  is  as  follows  :  If  required  to  burn 
any  given  time,  say  four  seconds,  the  case  is  cut  at  the  mark 
4,  exposing  the  ring  of  composition. 


FUZES  AND   PRIMERS.  333 

This  composition  then  burns  in  both  directions ;  but  hav- 
ing no  communication  with  the  chamber  e,  in  the  direction 
toward  5,  it  will  burn  for  four  seconds,  and  then  fire  the 
charge. 

The  objections  to  the  fuze  are : 

1.  Its  time  of  burning  is  too  short  for  modern  ranges ; 

2.  It  is  difficult  to  ignite  by  the  flame  from  the  charge  ; 

3.  If  once  cut,  it  cannot  be  used  for  a  greater  time  of  flight. 
The  modern  time  fuze  is  not  used,  except  in  combination 

with  the  percussion  fuze. 

185.  Percussion  Fuzes — Requisites— Essential  Parts. 

A  percussion  fuze  is  one  which  is  prepared  for  action  by 
the  shock  of  discharge,  and  which  acts  by  the  impact  of  the 
projectile. 

REQUISITES. — The  requisites  of  a  good  percussion  fuze 
are,  that  it  shall  be  safe  in  handling,  and  certain  in  its  opera- 
tion. 

Safety  in  Handling. — This  requires  : 

1.  A  safety  device  which  will  prevent  accidental   dis- 
charge in  store,  transportation  and  handling,  or  from  acci- 
dental shock,  such  as  dropping  the  projectile. 

2.  A  safety  device  which  will  prevent   accidental   dis- 
charge in  loading,  and  which  will  be  released  only  on  firing 
the  piece. 

These  may  be  combined  in  one,  as  will  be  seen  later. 
Certainty  of  Action. — This  requires  : 

1.  That  all  the  parts  of  the  fuze  be  protected  from  clog- 
ging, by  the  action  of  the  bursting-charge  in  transportation, 
and  by  other  causes,  such  as  dust,  etc. 

2.  A  safety  device  which  will  prevent  relative  motion  of 
the  parts  of  the  fuze  during  flight. 

ESSENTIAL  PARTS. — The  essential  parts  of  every  percus- 
sion fuze  are  : 

A  case,  to  contain  all  the  moving  parts  and  protect  them  ; 

A  plunger,  which  is  moved  backward  or  forward  on  im- 
pact, and  which  fires  the  fulminating  composition  ; 

A  fulminating  composition,  which  is  fired  by  the  impact 
of  the  plunger; 


334  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  priming,  which  is  a  charge  of  powder  ignited  by  the 
fulminate,  and  which  ignites  the  bursting-charge; 
A  safety  device  in  transportation ; 
A  safety  device  in  loading ; 
A  safety  device  in  flight. 

186.  Percussion  Fuzes  in  IT.  S.  Service — Classification — Hotchkiss 

Front  Percussion  Fuze — Action  of  Fuze — Safety  Devices. 
CLASSIFICATION. — Percussion  fuzes  are  classed  accord- 
ing to  the  position  they  occupy  in  the  projectile,  as : 

1.  Front  fuzes,  which  are  inserted  in  the  head  of  the  pro- 
jectile, at  the  point  of  the  ogive; 

2.  Base  fuzes,  which  are  inserted  in  the  centre  of  the  base. 
The  front-fuze  is  sometimes  used   with  field  projectiles, 

and  generally  when  penetration  is  not  required. 

The  base  fuzes  are  used  with  armor-piercing  projectiles, 
and  generally  where  penetration  is  required,  and  where  the 
head  of  the  projectile  must  have  great  resistance. 

The  front  fuze  has  the  advantage  of  having  the  bursting 
charge  of  the  projectile  thrown  toward  it  on  impact,  and 
there  is  no  danger  of  the  flame  from  the  charge  in  the  gun 
entering  the  cavity  of  the  projectile,  and  causing  premature 
explosion. 

The  percussion  fuzes  used  in  the  U.  S.  service  are  the 
Hotchkiss  Front  an'd  Hotchkiss  Base  Fuzes,  or  modifica- 
tions of  them. 

HOTCHKISS  FRONT  PERCUSSION  FUZE. — This  fuze  con- 
sists of  a  brass  case,  a,  Fig.  193,  threaded  on  the  exterior  for 
screwing  into  the  projectile.  The  upper  end  is  closed  by  a 
screw  cap,  b,  carrying  a  projecting  point,  c.  In  the  case  a,  is 
a  plunger,  d,  composed  of  a  brass  case,  e,  and  a  lead  body,/, 
in  which  is  a  brass  wire,  g.  The  central  part  of  the  lead 
body  carries  the  priming  charge  of  powder,  h,  and  on  the 
top  of  this  priming  is  the  fulminate,  i.  The  brass  case  e, 
encloses  the  lead  body/,  to  prevent  the  upsetting  laterally 
of  the  plunger,  by  the  shock  of  discharge,  and  its  conse- 
quent wedging  in  the  fuze-case. 

When  the  plunger  is  inserted  in  the  case  a,  the  brass 
wires  g,  occupy  the  position  shown,  and  the  rear  end  of  a  is 


FUZES  AND    PRIMERS. 


335 


closed    by   a   conical    lead    plug,  /,   bearing    against    the 
wires. 


ACTION  OF  FUZE. — When  the  piece  is  fired,  the  shock  of 
discharge  causes  the  lead  plug/  to  be  dislodged  from  its 
seat  in  the  fuze,  and  to  fall  into  the  cavity  of  the  projectile. 
The  plunger  d  then  moves  to  the  rear,  and  rests,  during 
flight,  upon  the  shoulder  k,  at  the  bottom  of  the  fuze  cavity. 
Upon  impact,  the  plunger  d  is  thrown  forward,  the  fulmi- 
nate *,  striking  the  pointy  and  thus  firing  the  priming 
charge  k,  which  fires  the  bursting  charge. 

SAFETY  DEVICES  IN  TRANSPORTATION  AND  LOADING. — 
These  are  combined  in  this  fuze,  and  are  formed  by  the 
conical  lead  plug,  bearing  on  the  brass  wire  g. 

SAFETY  DEVICE  IN  FLIGHT. — In  all  percussion-fuzes,  the 
plunger  has  a  tendency  to  move  forward  in  the  fuze  cavity 
during  flight.  This  is  due  to  the  fact  that  the  projectile  is 
retarded  by  the  resistance  of  the  air,  while  the  plunger,  not 
being  subjected  to  this  action,  is  not  affected  by  it,  and  its 
only  retarding  force  is  friction,  which  is  very  small.  If  the 
plunger  moves  forward,  it  will  either  explode  the  fulminate 
during  flight,  or  else  if  the  sensitiveness  of  the  fulminate  be 
diminished  to  prevent  this,  it  will  be  so  close  to  the  point  c,  on 
impact,  that  it  may  not  acquire  energy  sufficient  to  cause 
the  explosion  at  that  time.  In  this  fuze,  the  safety  device 
in  flight,  is  provided  by  the  wires  g,  which  spread  out- 


336 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


ward  when  the  lead  plug  j  is  dislodged,  and   thus  prevent 
the  forward  motion  of  the  plunger  till  impact. 

187.  Hotchkiss  Base   Percussion  Fuze  —  Action  of  Fuze  —  Safety 

Devices. 

HOTCHKISS  BASE  PERCUSSION  FUSE. — The   Hotchkiss 
base  percussion  fuze  consists  of  a  brass  case,  a,  Fig.   194,, 


of  the  shape  shown.  It  is  threaded  on  the  exterior  at  b, 
for  screwing  into  the  projectile,  and  on  the  interior  at  c, 
for  the  cap,  which  carries  the  fulminate.  The  flanges  at  d 
are  made  thin,  to  act  as  a  gas-check,  and  prevent  the  en- 
trance of  the  gas  from  the  charge  of  the  gun  into  the  fuze- 
cavity,  thus  prematurely  exploding  the  projectile. 

In  the  case  a  is  a  plunger,  e,  composed  of  a  brass  jacket, 
fj  a  lead  body,  £*,  and  a  firing-pin,  h.  The  combination  of 
lead  and  brass  is  for  the  purpose  previously  described.  The 
firing-pin,  h,  is  made  of  steel,  roughened  on  the  outside,  and 
the  lead  body  is  cast  around  it,  so  that  before  firing  its  point 
is  slightly  below  the  upper  surface  of  the  plunger. 

The  upper  part  of  the  fuze-case  carries  the  screw  cap  z, 
which  is  composed  of  the  party,  which  screws  into  the  fuze- 
case,  the  fulminate  k,  the  screw  cap  /  closing  j,  and  the 
safety  disk  of  copper  m. 

ACTION  OF  THE  FUZE. — When  the  piece  is  fired,  the 
shock  of  discharge  causes  the  heavy  plunger  e  to  slide  to  the 
rear  along  the  pin  h,  taking  the  position  shown  in  Fig.  195. 


FUZES  AND    PRIMERS. 


337 


The  action  of  the  brass  casing  of  the  plunger  is  to 
prevent  the  spreading  of  the  lead  body,  and  consequently 
cause  the  latter  to  take  a  firm  hold  on  the 
firing- pin. 

When  the  projectile  strikes,  the  plun- 
ger is  thrown  forward,  the  point  of  the 
firing-pin  passing  through  the  hole  n  in 
the  screw  cap,  strikes  and  explodes  the 
fulminate,  the  flame  from  which  passes 
through  the  hole  o  into  the  interior  of  the 
projectile,  and  ignites  the  bursting-charge. 

SAFETY  DEVICES  IN  TRANSPORTATION 
AND  LOADING. — These  are  combined  in 
this  fuze  and  consist  of :  FlG-  r95. 

1.  The  projecting  pin  h  being  held  firmly  in  the  lead; 
body  of  the  plunger,  with  its  point  below  the  upper  surface 
of  the  latter,  so  that  it  requires  the  shock  of  discharge  to 
force  the  plunger  down  over  the  pin,  and  allow  its  point 
to  project. 

2.  Making   the  lengths  of    the   plunger  and  projecting 
portion  of  the  pin  h  such,  that  before  firing  they  are  held 
tightly  in  position  in  the  case,  and  hence  the  plunger  cannot 
acquire  any  motion  which  might  force  it  along  the  pin. 

SAFETY  DEVICE  IN  FLIGHT.— This  is  provided  by  the 
copper  disk  m  on  the  bottom  of  the  fulminate  cap,  so  that 
if  the  point  of  the  pin  should  touch  the  cap  in  flight,  it  will 
not  cause  an  explosion. 

188.  Combination  Fuzes  —  Requisites  —  Frankford  Arsenal  Com- 
bination Fuze— Action  of  Fuze. 

A  combination  fuze  is  one  which  contains  both  a  time* 
and  a  percussion  fuze  in  the  same  case,  and  is  intended  to- 
increase  the  chances  of  bursting  the  projectile,  and  of  readily 
and  quickly  varying  the  kind  of  fire. 

REQUISITES. — A  good  combination  fuze  must  combine 
the  requisites  of  both  time  and  percussion  fuzes,  without 
being  too  bulky  or  too  expensive. 

THE  FRANKFORD  ARSENAL  COMBINATION  FUZE. — This 
fuze  is  used  in  the  U.  S.  service  for  field  shrapnel,  and  con- 
sists (Fig.  196)  of  a  case,  a,  of  bronze,  the  front  portion  of 


338 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


which  carries  the  time  fuze,  and  the  rear  portion  the  pen 
cussion  fuze. 

The  time  fuze  is  composed  of  the  plunger  b,  the  firing. 


r-v 


FIG.  196. 


pin  c,  the  cone  d,  the  time-train  e,  the  cover  /,  cap  g,  and 
clamping-nut  h. 

The  plunger  b  is  cylindrical  in  shape,  and  contains  the 
j-^-]  fulminate  i,  in  a  recess  at  its  base.     Its  upper 

extremity  is  pierced  to  receive  a  safety-pin,/, 
and  there  are  five  radial  lugs,  k,  Fig.  197,  which 
support  the  plunger  on  the  top  of  the  fuze 
body,  and  prevent  it  from  falling  against  the 
firing-pin  c,  when  the  safety  -  pin  at  j  is  re- 
moved, before  loading. 

The  firing-pin  c  is  of  steel,  inserted  into  the 
body  of  the  fuze  at  the  bottom  of  the  plunger 
channel. 

The  cone  d  is  an  alloy  of  soft  metal,  held  in 
place  on  the  fuze-body  by  the  clamping-nut  h,  and  a  groove 


FIG.  197. 


FUZES  AND    PRIMERS.  339 

m  at  the  bottom,  and  is  prevented  from  turning  by  a  steel 
pin,  /. 

The  lip  m  on  the  bottom  of  the  cone,  entering  the 
groove  in  the  body,  acts  as  a  gas-check  to  prevent  ignition 
of  the  powder  in  the  tube  n.  On  the  exterior  of  the  cone  d, 
is  a  left-handed  groove  which  carries  the  time-train  <?,  and 
this  time-train  communicates  at  its  lower  end  with  the 
priming-charge  in  the  tube/z,  and  thence  with  the  chambers. 

The  time-train  e  is  formed,  as  previously  described,  of  a 
lead  tube,  filled  with  mealed  powder,  and  wire-drawn. 

The  cover /is  of  brass,  arid  is  held  in  place  by  the  cap  g, 
and  prevented  from  turning  by  a  small  pin  projecting  from 
the  body  a,  and  fitting  in  a  slot  in  its  lower  edge.  On  the 
exterior  of  the  cover  is  a  left-handed  groove,  corresponding 
to  that  on  the  time-cone  d,  and  this  groove  is  pierced  with 
holes  numbered  from  I  to  15,  corresponding  to  the  number 
of  seconds,  the  spaces  between  the  holes  being  divided  into 
five  equal  parts. 

The  percussion  fuze  is  a  modification  of  the  Hotchkiss 
base  fuze  previously  described,  and  consists  of  the  primer 
in  front ;  a  plunger-spindle,  u,  carrying  a  firing-pin,  #';  a 
plunger-sleeve,  v\  a  safety-ring  of  brass,  w\  and  a  safety- 
disk  of  copper,  / ;  the  fuze  being  closed  in  rear  by  the  screw- 
plug  s,  and  this  screw-plug,  and  the  exterior  of  the  plunger 
sleeve  v,  being  grooved  longitudinally,  for  the  passage  of 
the  flame  from  the  chamber  o  to  the  bursting-charge. 

ACTION  OF  FUSE. — i.  As  Time  Fuse. — Suppose  the  fuze 
is  to  burn  12  seconds.  A  hole  is  punched  through  the 
cover,  time-train,  and  cone,  into  the  interior  of  the  fuze,  at 
the  i2-seconds  mark.  Just  before  loading,  the  safety  pin  is 
removed  from  the  hole/.  This  allows  the  time  plunger  b  to 
rest  on  the  top  of  the  fuze-body,  where  it  is  held  by  the  five 
radial  lugs,  k.  The  projectile  is  now  inserted  in  the  gun. 
By  the  shock  of  discharge  these  five  lugs  are  broken,  and  the 
time-plunger  b  is  thrown  to  the  rear,  its  primer  striking  the 
firing-pin  c,  which  explodes  the  fulminate.  The  flame  from 
the  fulminate  passes  through  the  four  radial  holes  /,  at  the 
base  of  the  fuze  body,  and  ignites  the  ring  of  compressed 
powder  q.  The  flame  from  this  powder,  ignites  the  fuze 


34°  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

composition  at  the  hole  marked  12,  which  has  been  punched 
through  the  time-cone  d,  and  after  burning  for  twelve  sec- 
onds, this  ignites  the  priming  charge  in  the  tube  n  and 
chamber  o.  The  flame  from  this  charge  passes  down  along 
grooves  r  in  the  percussion  fuze  body  and  screw  s,  and 
ignites  the  charge. 

2.  As  a  Percussion  Fuze. — When  the  piece  is  fired,  the 
plunger  sleeve  v  slides  relatively  to  the  rear,  against  the 
resistance  of  the  safety  ring  w,  and  this  ring  is  pushed  from 
its  groove,  and  along  the  spindle  u.  When  the  plunger 
sleeve  v  reaches  its  extreme  rear  position,  the  safety  ring  w 
slips  into  the  groove  wf,  and,  as  its  diameter  has  been  in- 
creased by  passing  over  the  plunger  spindle,  it  now  fits  into 
the  groove  in  the  plunger  sleeve,  and  locks  the  spindle  and 
sleeve  together.  '  The  point  of  the  firing-pin  u'  now  pro- 
jects beyond  the  plunger  sleeve,  and  on  impact,  the  sleeve 
and  spindle  are  thrown  forward,  exploding  the  primer. 

Safety  Device  in  Transportation. — The  safety  pin/,  for  the 
time-fuze,  and  the  plunger  sleeve  v,  and  safety  ring  w,  for 
the  percussion  fuze. 

Safety  Device  in  Loading. — The  radial  lugs  k  for  the  time 
fuze,  and  the  sleeve  and  ring,  as  before,  for  the  percussion 
fuze. 

Safety  Device  in  Flight:  Percussion  Fuze. — The  copper 
disk  /. 

189.  Delayed-action  Fuzes— The  Merriam  Delayed-action  Fuze- 
Action  of  Fuze. 

A  delayed-action  fuze  is  one  which  is  prepared  for  action 
by  the  shock  of  discharge,  and  whose  final  action  is  retarded 
till  the  projectile  has  passed  through  the  object  or  reached 
a  certain  position  where  its  explosion  will  be  most  effective. 

THE  MERRIAM  DELAYED-ACTION  FUZE. — The  principles 
of  this  class  of  fuzes  will  be  best  explained  by  the  descrip- 
tion of  one  of  them  which  has  been  tried — the  Merriam  Fuze. 

This  fuze  consists  of  a  case  ®r  body,  a,  Fig.  198, 
threaded  on  the  exterior  for  screwing  into  the  base  of 
the  projectile.  In  the  interior  of  the  case  are  a  ham- 
mer, b,  in  the  form  of  a  sphere,  held  in  place  by 


FUZES   AND    PRIMERS. 


341 


clips,  c,  which  abut  against  a  shoulder  in  the  case  and  a 
circular  recess  in  the  ball  b ; 
two  pistons,  d,  which  are 
forced  forward  by  the  press- 
ure of  the  gas  of  the  powder- 
charge  in  the  gun ;  a  flat 
spring,  e,  which  keeps  the  ball 
in  place  during  flight;  three 
small  balls,/,  which  are  held 
firmly  in  their  seats  below 
three  percussion-caps,  g\  a 
valve,  h,  in  front,  which 
moves  parallel  to  the  axis  of 
the  fuze,  and  carries  on  its 
forward  face  a  ring,  z,  of  com- 
pressed powder ;  four  radial 

chambers,  /  carrying   priming-charges  of   powder,  and  a 
screw,  k,  whose  use  will  be  explained. 

ACTION  OF  FUZE. — When  the  piece  is  fired,  the  pressure 
of  the  gas  pushes  forward  the  two  pistons  d,  and  these, 
striking  the  clips  c,  push  them  off  the  shoulders  in  the  case. 
The  ball  b,  is  thus  left  free  to  move  forward,  but  is  pre- 
vented from  doing  so  in  flight,  by  the  flat  spring  e.  When 
the  projectile  strikes  the  object,  such  as  an  armor-plate,  the 
ball  b  is  thrown  forward,  and,  striking  one  of  the  small  balls 
/  drives  it  against  its  percussion-cap,  exploding  it.  The 
flame  from  this  cap  passes  into  the  chamber  /. 

When  the  ball  b  is  thrown  forward  by  the  striking  of  the 
projectile,  the  valve  h  also  moves  forward  at  the  same  time, 
and  bears  against  the  front  of  the  fuze-case,  thus  closing  the 
openings  oo  which  communicate  with  the  priming-charges 
in  the  chambers/  The  valve  h  reaches  its  seat  against  the 
front  of  the  case  before  the  ball  b  explodes  the  caps  g,  be- 
cause it  has  a  shorter  distance  to  travel.  The  flame  from 
the  percussion-caps,  entering  the  chamber  /,  ignites  the  com- 
pressed powder  ring  t,  but,  as  this  ring  of  powder  is  held 
between  two  closely-fitting  surfaces,  it  can  burn  only  on 
the  edge.  As  long  as  the  projectile  is  passing  through  the 
plate,  or  until  it  stops  in  the  plate,  it  is  being  retarded,  and 


342  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

the  acquired  energy  of  the  valve  will  keep  it  in  contact  witb 
the  front  face  of  the  fuse.  As  soon,  however,  as  the  projec- 
tile passes  through  the  plate,  or  stops  in  it,  the  valve  h  will 
move  back  and  open  the  holes  o  o,  and  the  charge  will  be 
tired.  The  screw  k,  holds  back  the  valve  h,  when  screwed 
down,  and  there  is  no  delayed  action  in  this  case. 

PRIMERS. 

190.  Definition  —  Classification  —  Requisites  —  Common  Friction- 
Primer — Action. 

DEFINITION. — Primers  are  the  means  employed  to  ignite 
the  powder-charge  in  a  gun. 

CLASSIFICATION. — Primers  are  classified  according  to  the 
method  by  which  they  are  fired,  into— 

1.  Friction  ; 

2.  Electric  ; 

and  each  of  these  may  be  either  common  or  obturating. 

A  common  primer  is  one  which  ignites  the  charge,  and 
is  blown  out  of  the  vent,  allowing  the  gas  of  the  charge  to 
escape  through  the  latter. - 

An  obturating  primer  is  one  which  remains  seated  in  the 
vent  at  discharge,  and  prevents  the  escape  of  gas  through 
the  vent. 

The  primers  used  with  small-arm  ammunition  will  be 
explained  later.  Those  used  with  cannon  are  described 
here. 

REQUISITES. — Primers  should  be  safe  in  handling,  not 
liable  to  damage  or  accident  in  store,  and  certain  in  action. 

The  requisite  of  safety  in  handling  prevents  the  use  of 
mercuric  fulminate,  except  in  the  small-arm  primers.  As  a 
general  rule  mercuric  fulminate  cannot  be  used  where  it  is 
exposed  to  friction  of  any  kind.  Hence  in  fuzes  it  may  be 
safely  used,  since  all  the  parts  are  relatively  fixed,  and  well 
protected  ;  but  this  is  not  the  case  with  primers. 

COMMON  FRICTION  PRIMER.— This  primer,  (Fig.  199),  is 
composed  of  two  copper  tubes,  a  and  b,  at  right  angles  to 
each  other  ;  a  copper  wire,  c,  flattened  and  roughened  at  one 
end ;  a  charge  of  powder  filling  the  tube  a ;  and  a  friction 


FUZES  AND    PRIMERS. 


343 


composition  of  antimony  sulphide  and  potassium  chlorate, 
filling  the  tube  b. 

The  tubes  a  and  b  are  each  made  from  copper  disks,  a' 
and  £',  by  the  successive  action  of  punches  and  dies,  by 
which  the  diameter  and  thickness  of  the  tubes  are  decreased, 
and  their  length  increased,  as  shown  in  the  figure.  After 
the  proper  length  and  diameter  of  each  have  been  obtained, 
a  hole  is  drilled  in  the  side  of  the  tube  a,  near  its  head,  the 


a 


FIG.  199. 

tube  b  soldered  to  #,  the  wire  c  inserted  through  the  hole 
in  a,  its  rough  end  resting  in  the  tube  b,  which  is  then  filled 
with  the  friction  composition  in  a  moist  state,  and  the  end 
of  b  closed  on  the  wire,  to  hold  the  latter  in  place.  The  tube 
a  is  filled  with  small-arms  powder,  and  its  lower  end  closed 
with  a  wad  of  wax.  The  outer  end  of  the  wire  c  is  formed 
into  a  loop,  for  the  attachment  of  the  hook  of  the  lanyard. 

ACTION. — When  the  wire  is  pulled  by  the  lanyard,  the 
roughened  edges  fire  the  friction  composition  in  the  tube  b> 
and  this  ignites  the  powder  in  a. 

191.  Common  Electric  Primer— Action. 

It  is  often  necessary  to  fire  at  a  distance  from  the  gun, 
as  in  experiments  ;  or  from  a  central  station  where  the  ob- 


344 


TEXT-BOOK  OF  ORDNANCE  AND   GUNNERY. 


ject  can  be  plainly  seen ;  or  where  all  the  guns  of  a  battery 
are  to  be  fired  simultaneously. 

For  this  purpose  the  electric  primer  is  used. 


FIG.  200. 

COMMON  ELECTRIC  PRIMER.  —  The  common  electric 
primer  (Fig.  200),  consists  of  two  copper  tubes,  a  and  b, 
and  two  insulated  copper  wires,  c,  joined  at  one  end  by  a 
small  platinum  wire,  f. 

These  wires  are  inserted  in  a  plug  of  wood,  d,  and  are 
surrounded  by  a  small  quantity  of  dry  gun-cotton,  e.  This 
plug  of  wood,  with  its  wires  and  gun-cotton,  is  inserted  into 
the  tube  a,  and  the  outer  end  is  closed  down  to  hold  it  in 
place,  and  the  opening  filled  with  wax.  The  tube  b  is  in- 
serted in  a  beforehand,  and  soldered  to  it,  as  shown  in  the 
figure,  and  is  then  filled  with  small-arms  powder,  and  the 
open  end  closed  with  wax. 

ACTION. — When  the  circuit  is  closed,  the  current  heats 
the  fine  platinum  wire,  ft  and  this  fires  the  gun-cotton, 
which  fires  the  powder  in  the  tube  b. 

192.  Obturating  Friction  Primer — Action. 

With  large  guns,  the  long-continued  action  of  the  gases 
under  high  pressure,  erodes  the  vent  rapidly,  if  allowed  to 
issue  freely  through  it,  and  hence  an  obturating  primer  is 
necessary  for  these  guns. 

OBTURATING  FRICTION  PRIMER. — The  obturating  fric- 
tion primer  (Fig.  201),  consists  of  a  case,  a,  threaded  on  the 


FUZES  AND    PRIMERS. 


345 


exterior  at  b,  to  screw  into  the  vent.  A  shoulder,  c,  limits 
the  extent  to  which  the  case  can  be  inserted.  At  the  rear 
end,  d,  the  case  is  square,  to  give  a  purchase  for  screwing  it 
in  and  removing  it.  On  the  interior,  the  case  is  pierced 
with  the  hole  e  for  the  passage  of  the  wire/.  This  passage 
is  enlarged  in  front  and  has  a  cone-shaped  surface  at  g. 
The  front  of  the  case  is  made  thin  at  h,  for  a  reason  to  be 
given  later.  The  other  parts  of  the  primer  are  a  brass  wire, 


V  *'  x'"      f 


FIG.  201. 

y,  roughened  at  its  forward  end,  and  having  a  conical  sleeve, 
/,  loose  upon  it,  and  a  conical  enlargement,  i' ' . 

Upon  this  wire  is  secured  pellet  of  friction-composition, 
/,  and  these  parts,  when  inserted  into  the  primer-case,  occupy 
the  positions  shown ;  the  rear  end  of  the  wire  being  twisted 
into  a  loop,  for  the  attachment  of  the  hook  of  the  lanyard. 

The  front  part  of  the  case  is  filled  with  small-arms  pow- 
der. 

ACTION. — The  primer  is  inserted  into  the  vent  and 
screwed  home,  till  stopped  by  the  shoulder  c.  When  the 
wire  is  pulled  to  the  rear  by  the  lanyard,  the  roughened 
end  fires  the  pellet  of  friction-composition  /,  and  this  fires 
the  priming  charge. 

The  gas  may  escape  in  two  ways :  first  along  the  outside 
of  the  case  and  around  the  screw-thread  ;  second,  through 
the  hole  e  in  which  the  wire  rests. 

To  prevent  escape  along  the  outside,  the  thin  part  of  the 
case  h,  in  front,  expands  under  pressure,  and  fits  tightly 
against  the  walls  of  the  vent,  thus  forming  a  perfect  gas- 
check.  To  prevent  escape  through  the  hole  e,  the  drawing 
back  of  the  wire  f,  in  firing,  brings  the  conical  enlargement 


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TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


i'  firmly  against  the  front  of  the  sleeve  2,  and  the  latter 
against  its  conical  seat,  g,  in  the  case,  and  the  gas-pressure 
keeps  it  in  place,  thus  closing  the  hole  e. 

193.  Obturating  Electric  Primer — Action. 

OBTURATING  ELECTRIC  PRIMER. — This  primer  is  used 
for  the  same  reasons  as  the  common  electric  primer,  and  con- 


FIG.  202. 

sists,  (Fig.  202),  of  a  case,  a,  exactly  similar  on  the  exterior  to 
that  of  the  obturating  friction  primer  just  described.  On 
the  interior,  the  forward  part  of  the  case  b  is  made  thin  to 
serve  as  a  gas-check,  as  before  explained.  A  seat,  of  the 
shape  shown  at  c,  is  made  near  the  middle  of  the  case,  and  a 
hole,  d,  allows  the  wires  e  to  pass  through.  The  other  parts 
of  the  primer  are,  the  two  insulated  wires,  e,  passing  through 
a  hard  rubber  plug,  /,  and  connected  at  their  forward  ends 
by  a  piece  of  platinum  wire,  g.  A  small  piece  of  gun-cotton, 
h,  is  wound  round  the  platinum  wire,  and  the  whole  inserted 
in  the  primer  case,  occupying  the  position  shown. 

The  front  of  the  primer  case  is  filled  with  small-arms 
powder. 

ACTION. — When  the  circuit  is  closed,  the  current  heats 
the  platinum  wire  g,  and  this  fires  the  gun-cotton  h,  which 
in  turn  ignites  the  powder  in  the  front  of  the  primer  case. 

The  escape  of  gas  around  the  outside  of  the  primer  is 
prevented  by  the  expansion  of  the  thin  portion  of  the  case 
in  front,  as  before.  The  escape  through  the  hole  d  is  pre- 
vented by  the  hard  rubber  plug  fy  which  is  forced  into  its 
seat  by  the  pressure. 


CHAPTER  VI. 

EXTERIOR  BALLISTICS. 

194.  Definitions. 

Exterior  Ballistics  treats  of  the  motion  of  a  projectile  in 
air,  after  it  has  left  the  piece. 

The  Trajectory,  a,  Fig.  203,  is  the  curve  described  by 
the  centre  of  gravity  of  the  projectile  during  its  passage 
through  the  air. 


FIG.  203. 

,  • 

The  Line  of  Fire,  be,  is  the  prolongation  of  the  axis  of  the 
piece. 

The  Plane  of  Fire  is  the  vertical  plane  containing  the  line 
of  fire. 

The  Line  of  Sight,  def,  is  the  straight  line  passing  through 
the  sights  and  the  point  aimed  at. 

The  Plane  of  Sight  is  the  vertical  plane  containing  the  line 
of  sight. 

The  Angle  of  Sight,  s,  is  the  angle  made  by  the  line  of 
sight  with  the  horizontal. 

347 


34**  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  Angle  of  Departure,  g! ,  is  the  angle  made  by  the  line 
of  departure  with  the  horizontal. 

The  Angle  of  Elevation,  0,  is  the  angle  made  by  the  axis 
of  the  piece  with  the  horizontal. 

The  angle  of  elevation  generally  differs  slightly  from  the 
angle  of  departure,  owing  to  the  movement  of  the  gun  at 
discharge.  This  movement  is  due  to  the  elasticity  of  the 
parts  of  the  carriage,  and  the  lack  of  accurate  fitting  of  the 
trunnions  in  their  beds,  the  play  of  the  elevating  device,  etc. 
The  Jump,  j,  is  the  difference  between  the  angle  of  de- 
parture and  of  elevation,  and  must  be  determined  by  exper- 
iment. 

The  Angle  of  Fall,  GO,  is  the  angle  made  by  the  tangent  to 
the  trajectory  with  the  horizontal  at  the  end  of  the  range. 

The  Range,  bh,  is  the  horizontal  distance  from  the  muzzle 
to  the  point  where  the  projectile  strikes. 

Initial  Velocity  is  the  velocity  of  the  projectile  at  the 
muzzle. 

Remaining  Velocity  is  the  velocity  of  the  projectile  at  any 
point  of  the  trajectory. 

Final  Velocity  is  the  velocity  of  the  projectile  at  the  end 
of  the  range. 

Drift,  kf,  is  the  departure  of  the  projectile  from  the 
plane  of  fire,  due  to  the  resistance  of  the  air,  and  the  rotation 
of  the  projectile. 

Direct  Fire  is  from  guns,  with  service  charges,  at  all 
angles  of  elevation  not  exceeding  15°. 

Indirect  or  Curved  Fire  is  from  guns,  with  less  than  service 
charges,  and  from  howitzers  and  mortars,  at  all  angles  of 
elevation  not  exceeding  15°. 

High-angle  Fire  is  from  guns,  howitzers,  and  mortars  at 
all  angles  of  elevation  exceeding  15°. 

195.  Forces  Acting  on  a  Projectile  —  Circumstances  of  Motion  — 

Drift. 

FORCES  ACTING.— In  the  case  of  an  oblong  projectile, 
which  is  the  only  one  considered,  a  motion  of  rotation  about 
its  longer  axis  is  given  to  it,  by  the  rifling  of  the  gun,  as  it 
passes  through  the  bore.  When  it  leaves  the  bore,  it  is  sub- 


EXTERIOR   BALLISTICS.  349 

jected  to  the  action  of  gravity,  and  the  resistance  of  the  air. 
It  is  therefore  a  free  body,  having  a  motion  of  translation 
and  of  rotation  impressed  upon  it,  and  acted  on  by  the  two 
forces  above  mentioned. 

CIRCUMSTANCES  OF  MOTION. — The  exact  motion  of  the 
projectile  under  these  circumstances  is  very  complex,  and 
is  discussed  in  mechanics  under  the  subject  of  "  Rotation." 

The  general  result  of  the  action  of  the  forces  may  be 
stated  as  follows : 

When  the  projectile  first  issues  from  the  piece,  its  longer 
axis  is  tangent  to  the  trajectory.  The  resistance  of  the  air 
acts  along  this  tangent,  and  is  at  first  directly  opposed  to 
the  motion  of  translation  of  the  projectile,  and  hence  its 
resultant  coincides  with  the  longer  axis,  and  it  exerts  no 
effort  to  overturn  the  projectile  about  its  shorter  axis. 

The  longer  axis  of  the  projectile,  being  a  stable  axis  of 
rotation,  tends  to  remain  parallel  to  itself  during  the  passage 
of  the  projectile  through  the  air,  but  the  tangent  to  the 
trajectory  changes  its  inclination,  owing  to  the  action  of 
gravity.  The  resistance  of  the  air  acting  always  in  the 
direction  of  the  tangent,  thus  becomes  inclined  to  the  longer 
axis  of  the  projectile,  and  for  projectiles  in  our  service,  and 
modern  projectiles  generally,  its  resultant  intersects  the 
longer  axis,  at  a  point  in  front  of  the  centre  of  mass. 

In  Fig.  204,  G  being  the  centre  of  mass,  and  R  the  re- 


FIG.  204. 

sultant  resistance  of  the  air,  this  resultant  acts  with  a  lever- 
arm  /,  to  rotate  the  projectile  about  a  shorter  axis  through 
G,  perpendicular  to  the  plane  of  fire. 

If  the  projectile  possesses  sufficient  energy  of  rotation 
about  its  longer  axis  under  these  circumstances,  the  rotation 
about  the  shorter  axis  will  not  occur,  but  the  practical  re- 
sult will  be,  that  for  projectiles  rotating  from  left  to  right,  as 


35°  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

in  our  service,  the  point  of  the  projectile  will  move  slowly 
to  the  right  of  the  plane  of  fire.  As  soon  as  this  motion  of 
the  point  to  the  right  occurs,  it  causes  a  relative  change  in 
the  direction  of  the  resistance  of  the  air,  and  an  oblique 
pressure  is  produced  on  the  left  side  of  the  projectile,  by 
which  it  is  forced  sidewise  to  the  right,  out  of  the  plane  of 
fire.  At  the  same  time,  the  resultant  of  this  new  oblique 
pressure,  and  of  the  rotation,  causes  the  point  of  the  pro- 
jectile to  move  downward. 

The  result  of  the  continued  action  of  these  forces  is 
practically— 

1.  To  cause  the  axis  of  the  projectile  to  describe  a  cone 
about  the  tangent  to  the  trajectory. 

2.  To  force  the  projectile  bodily  to  the  right,  and  out  of 
the  plane  of  fire. 

DRIFT. — This  departure  of  the  projectile  from  the  plane 
of  fire,  due  to  the  causes  above  mentioned,  is  called  drift, 
and  may  be  computed  by  Mayevski's  formula,  which  will 
be  given  later.  The  actual  motion  of  the  projectile  is  more 
complex  than  that  above  given,  and  its  full  investigation 
requires  analytical  methods. 

196.  Form  of  Trajectory — Causes  Affecting  Resistance — Form — 
Cross-section — Density  of  the  Air. 

FORM  OF  TRAJECTORY. — From  the  above  it  appears,  that 
the  trajectory  is  not  a  plane  curve,  but  one  of  double  curva- 
ture. It  is  also  shown  by  analytical  methods,  that  the  drift 
increases  more  rapidly  than  the  range,  and  hence  the  pro- 
jection of  the  trajectory  on  the  horizontal  plane,  is  convex 
to  the  horizontal  projection  of  the  line  of  fire,  Fig.  203. 

The  trajectory  ordinarily  considered,  is  the  projection  of 
the  actual  curve  upon  the  vertical  plane  of  fire.  This  pro- 
jection so  nearly  agrees  with  the  actual  curve  that  the  re- 
sults thus  obtained  are  practically  correct,  and  the  advan- 
tage of  considering  it,  instead  of  the  actual  curve,  is,  that  we 
need  consider  only  that  component  of  the  resistance  of  the 
air  which  acts  directly  along  the  longer  axis  of  the  projec- 
tile, and  which  is  directly  opposed  to  the  motion  of  transla- 
tion. 


EXTERIOR  BALLISTICS.  35  I 

CAUSES  AFFECTING  RESISTANCE. — The  resistance  of  the 
air  to  the  motion  of  a  projectile  varies  with — 

1.  Its  form ; 

2.  Its  cross-section  ; 

3.  The  density  of  the  air; 

4.  The  velocity  of  the  projectile. 

FORM. — Experiment  shows  that  the  ogival  form  of  head 
offers  less  resistance  than  any  other,  and  the  radius  of  the 
ogive  has  been  increased  up  to  2  and  3  calibres.  Beyond 
this  latter  radius  other  considerations,  such  as  strength  to 
resist  deformation,  etc.,  enter.  The  resistance  depends 
principally  upon  the  form  of  the  head  near  its  junction  with 
the  cylindrical  body  of  the  projectile,  as  this  affects  the  flow 
of  the  air  over  the  projectile.  The  shape  of  the  rear  portion 
of  the  body  also  affects  the  resistance,  and  a  projectile  which 
is  barrel-shaped  in  rear,  such  as  the  Whitworth,  offers  less 
resistance  than  one  cylindrical  in  form,  for  the  same  reason 
as  above.  Practical  considerations  of  ease  of  manufacture, 
facility  of  packing,  etc.,  have,  however,  prevented  the  adop- 
tion of  the  Whitworth  shape. 

CROSS-SECTION. — Numerous  experiments  show  that  the 
resistance  of  the  air  varies  directly  with  the  area  of  cross- 
section  of  the  projectile. 

DENSITY  OF  THE  AIR. — Experiment  also  shows  that  the 
resistance  varies  directly  with  the  density  of  the  air,  and  as 
this  density  varies  with  the  temperature  and  pressure,  read- 
ings of  the  thermometer  and  barometer  must  be  taken,  when 
accurate  results  are  to  be  obtained.  These  readings  are 
used  to  calculate  the  densities,  as  will  be  explained. 

197.  Relation  between  Velocity  and  Resistance— Experiments. 

EXPERIMENTS. — The  relation  between  the  velocity  of  a 
projectile,  and  the  resistance  opposed  to  its  motion  by  the 
air,  has  been  the  subject  of  experiment  from  the  earliest 
times  to  the  present  day.  The  most  notable  experiments 
upon  this  subject  are  : 

i.  Robins  in  1742  made  the  first  experiments  by  means 
of  the  ballistic  pendulum  which  he  invented.  His  conclu- 
sions were,  that  up  to  iioo  ft.-secs.  the  resistance  is  propor- 


352  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

tional  to  the  square  of  the  velocity  ;  at  iioo  ft.-secs.  the  law 
of  the  resistance  changes;  beyond  1  100  ft.-secs.  the  resist- 
ance is  nearly  three  times  as  great  as  if  calculated  by  the 
law  of  the  lower  velocities. 

2.  Hutton  in  1790  improved  the  ballistic  pendulum,  and 
made   numerous  experiments   with  large  projectiles.     His 
conclusions  were,  that  the  resistance  increases  more  rapidly 
than  the  square  of  the  velocity  for  low  velocities,  and  for 
higher  velocities  that  it  varies  nearly  as  the  square. 

3.  General  Didion  made  a  series  of  experiments  at  Metz 
in   1839  and  1840  with  the  ballistic  pendulum,  and  spheri- 
cal projectiles  of  varying  weights.     His  conclusions  were, 
that  the  law  of  resistance  is  expressed  by  a  formula  of  the 
general  form 

R  oc 


a  and  b  being  constants.     This  formula  held  for  sh'ort  ranges, 
but  not  for  heavy  charges  and  high  angles  of  elevation. 

4.  Experiments  were  therefore  made  again  at  Metz  in 
1857,  and  with  electro-ballistic  instruments.     The  conclu- 
sions from  these  experiments  were,  that  the  resistance  varies 
as  the  cube  of  the  velocity.     Experiments  by  Prof.  Helie  at 
Gavre,  in  1860  and  1861,  gave  practically  the  same  result. 

5.  The  most  accurate  experiments  upon  this  subject  were 
made  by  the  Rev.  Francis  Bashforth  in  England,  in  1865,  and 
again  in  1880.     The  advantage  of  these  experiments  is  that 
they  were  made  with  a  very  accurate  instrument,  and  with 
comparatively    modern    projectiles.      The    conclusions    in 
general  were,  that  the  resistance  varies  with  some  power  of 
the  velocity,  and  that  this  power  varies  with  the  velocity, 
being  generally  as  follows  : 

For  velocities  between    900  and  1  100  ft.-secs  ......   v* 

11  "         between  iioo  and  1350  ft.-secs...  ...   v* 

"  "         above       1350  ft.-secs  ..............   v* 

6.  The  most  recent  experiments  on  the  subject,  and  those 
now  adopted  for  use,  were  made  by  Krupp  in   1881   with 
modern  guns,  projectiles,  and  velocities.     General  Mayevski 
discussed  the  results  of  these  experiments,  and  deduced  ex- 
pressions for  the  resistance  as  follows  : 


EXTERIOR   BALLISTICS.  353 

198.  Method  of  Determining  Resistance. 

The  resistance  of  the  air  is  a  force  expressed  in  pounds 
per  square  inch,  and  it  opposes  the  motion  of  the  projectile 
in  its  passage. 

The  effect  of  this  force  is  to  retard  the  projectile.  There 
are  therefore  two  quantities  to  be  determined : 

1.  The  resistance,  or  pressure  of  the  air,  in  pounds  per 
square  inch  ; 

2.  The  retardation,  or  loss  of  velocity  in  feet  per  second, 
produced  by  this  resistance. 

METHOD  EMPLOYED  TO  DETERMINE  RESISTANCE. — The 
method  generally  employed  to  determine  the  resistance  of 
the  air,  consists  in  measuring  the  velocities  vl  and  v^  of  the 
projectile,  at  two  points  Ml  and  M9 ,  situated  at  such  a  dis- 
tance apart,  that  the  path  of  the  projectile,  over  this  distance, 
may  be  regarded  as  a  right  line ;  and  also  so  that  the  resist- 
ance may  be  considered  constant  over  this  distance.  The 
energy  of  the  projectile  at  the  point  Ml  is  \mv*,  and  at 
M^ ,  \mv*.  Their  difference,  fyn(v?  —  v^],  is  the  loss  of 
energy  over  this  distance  due  to  the  resistance  of  the  air ; 
and  supposing  this  resistance  constant,  and  calling  the  re- 
sistance p,  and  the  path  /,  we  have 

pl  =  bn(v?  -  V?) (262) 

This,  being  the  mean  resistance,  corresponds  to  the  mean 

^+^Q 

velocity,  or  — - — 

By  properly  selecting  the  points,  and  varying  the  veloc- 
ity so  as  to  include  all  service  velocities,  we  obtain  a  series 
of  values  for  the  velocity  and  resistance,  from  which  a  curve 
can  be  constructed,  giving  the  law  of  resistance  for  different 
velocities. 

The  distance  between  M,  and  M^  must  be  chosen  accord- 
ing to  the  velocities  and  projectiles  used.  Thus  for  low 
velocities,  and  large  projectiles,  the  distance  between  the 
points  must  be  greater,  since  the  loss  of  velocity  over  a 
given  path  is  less  in  this  case,  than  for  small  projectiles 
moving  with  high  velocities. 


354  TEXT-BOOK  Of    ORDNANCE   AND    GUNNERY. 

199.  Modifications  of  General  Method — Results — Resistance. 

MODIFICATIONS. — When  the  curve  of  resistance  obtained 
by  the  above  general  method  is  plotted,  it  is  found  that 
sudden  changes  occur  in  it  for  different  velocities. 

Also  the  above  expression  does  not  take  account  of  vari- 
ation in  the  form  and  cross-section  of  the  projectile,  or  in 
the  density  of  the  air. 

To  have  a  general  expression  into  which  all  these  quan- 
tities enter,  General  Mayevski  proceeded  as  follows : 

Denoting  the  resistance  as  before  by  p,  the  retarda- 
tion is 

A       JL 

M  "  Wp' 

in  which  M  is  the  mass  of  the  projectile ; 
W,  its  weight  in  pounds ; 
g,  the  acceleration  of  gravity,  32.2  ft.-secs. 

A 
This  expression  was  placed  equal  to  -£-f(v\  in  which  A 

is  a  constant  to  be  determined  by  experiment,  C  a  factor 
called  the  "  ballistic  coefficient,"  and  f(v)  some  function  of 
the  velocity.  Hence  we  have 


The  Ballistic  Coefficient  C. — The  value  of  this  coefficient  is 


in  which 

£,  is  the  standard  density  of  the  air ; 

<S,  the  density  at  the  time  of  the  experiment ; 

c,  the  coefficient  of  reduction  ; 

d,  the  diameter  of  the  projectile  in  inches ; 
W,  its  weight  in  pounds  as  before. 

Substituting  the  value  of  C  from  (264)  in  (263),  we  have 

p  =  AfW (26s) 


EXTERIOR   BALLISTICS.  355 

For  a  given  projectile,  all  the  quantities  which  enter  the 
ballistic  coefficient  C  are  known,  and  they  take  into  account 
the  cross-section  and  weight  of  the  projectile,  and  the  den- 
sity of  the  air. 

The  form  of  the  projectile  enters  in  the  coefficient  of 
reduction  c  as  follows :  For  projectiles  of  a  standard  form, 
or  for  those  with  which  the  experiments  are  made,  the  coef- 
ficient of  reduction  is  taken  as  unity.  For  those  differing 
from  the  standard,  the  retardation  will  be  greater  or  less,  as 
the  form  is  less  or  more  suited  to  overcome  the  resistance. 
Hence  this  coefficient  will  have  values  greater  than  unity 
for  projectiles  whose  resistance  is  greater  than  the  standard, 
and  values  less  than  unity  for  those  whose  resistance  is  less 
than  the  standard.  For  the  older  forms  of  projectiles  in  our 
service  c  =  i,  for  the  new  form  c  =  0.9  nearly. 
$ 

The  values  of  —  for  all   pressures   and   temperatures   in 

practice  are  calculated  and  tabulated  for  use  in  Table  III 
(Ballistic  Tables). 

The  only  remaining  quantities  in  formula  (265)  are  A  and 
f(v\  and  the  object  of  the  experiments  is  to  determine  the 
values  of  A  and  the  exponent  of  v. 

RESULTS. — As  a  result  of  the  experiments,  the  general 
value  (265)  for  the  retardation  assumes  the  following  forms 
for  different  velocities  : 

For  all  velocities  greater  than  I33oft.-seconds, 

Jlp  =  -£,';     log  A  =4,  1525284; 
1330  ft.-secs.  >  v>  1 120  ft.-secs. 

WP  =  ~CV* '     log  A  =  7'°36435 1  ; 
1 1 20  ft.-secs.  >  v  >  990  ft.-secs. 

-j^rP^^6;     log  ,4   =^8865079; 
990  ft.-secs.  >  v  >  790  ft.-secs. 


356  TEXT-BOOK   OF   ORDNANCE   AND    GUNNERY. 

-^p  =  ~vz ;     log  A  =  8.8754872  ; 
790  ft.-secs.  >  v  >  100  ft.-secs. 
-j-p  =  ^v* ;     log  A  =  5.7703827. 

RESISTANCE. — The  corresponding   resistance  in  pounds 

W 

is  obtained  for  each  velocity  by  multiplying  by  —  since 

o 

6  cd*  '  "  \    .   .   .   (266) 


200.  Trajectory  in  Air — Nomenclature — Equations  of  Motion. 

NOMENCLATURE. — Considering  the  motion  of  translation 
only,  and  that  the  resistance  of  the  air  is  directly  opposed 
to  this  motion,  let  (Fig.  205). 


£ X -*  y 

2\—  "T 

FIG.  205. 

R  be  the  retardation  due  to  the  resistance  of   the  air,  its 
value  being  given  by  equation  (265) ; 

V,  the  initial  velocity  ; 

v,  the  velocity  of  any  point  of  the  trajectory  whose  co-ordi- 
nates are  x  and  y  ; 

z/j,  the  velocity  in  the  direction  of  x\ 

0,  the  angle  made  by  the  tangent  to  the  trajectory  with  the 
horizontal,  at  the  origin  ;  or  the  angle  of  elevation  ; 

0,  the  value  of  0  for  any  other  point  of  the  trajectory  ; 

x  and  y,  the  co-ordinates  of  any  point  of  the  trajectory,  in 
feet; 

X,  the  whole  range  in  feet. 

EQUATIONS  OF  MOTION. — The  only  forces  acting  on  the 

projectile  after  it  leaves  the  piece,  are  the  resistance  of  the 

air  and  gravity. 


EXTERIOR   BALLISTICS.  357 

The  resistance  of  the  air  is  directly  opposed  to  the  mo- 
tion of  the  projectile,  and  continually  retards  it.  Gravity 
is  supposed  to  act  vertically,  and  retards  the  projectile  in 
the  ascending  portion  of  the  trajectory,  while  it  accelerates 
it  in  the  descending-  portion. 

Considering  the  ascending  portion,  we  have  for  the  ac- 
celeration along  x,  since  gravity  has  no  component  in  that 
direction, 


',     ......     (267) 

from  this 

dv, 


The  velocity  along  x  is 
and  along  y, 


dx 

vi  =  j7  =  v  cos  6 ; (269) 


dy 

-^  =  v  sin  8  —  vl  tan  0  .....     (270) 

Substituting  the  value  of  dt  from  (268)  in  (269)  and  (270), 
we  have 


(27I) 


vl  tan  0  dv. 


Zcosd 
The  acceleration  along  the  radius  of  curvature  is 

v* 


Substitute  in   this   for  r  its  value  —  -^  from  calculus, 


(273) 
au 


and  we  have 

v*         ds  i  dsdB  dB 


0>  -  (274) 


358  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

hence 

gcosBdt 


(275) 


Substitute  in  (275)  for  cos  &  its  value  from  (267)  and  for 
v  its  value  from  (269),  and  we  have 


g  cos  6  dv. 


(276) 


Collecting  these  equations,  we  have 


dt  =  - 


dx—  - 


dv, 


1 


R  cos  B  ' 


R  cos  B  ' 


v.  tan  0  dv 
dy=-- 


dO  = 


R  cos  B     ' 
g  cos 


(A) 


If  these  equations  could  be  integrated  directly,  they  would 
give  the  values  of  x,  y,  t,  and  0  for  any  point  of  the  trajectory. 
But  as  they  are  expressed  in  terms  of  R,  vl9  and  B,  three  in- 
dependent variables,  the  direct  integration  is  impossible. 

201.  Method  of  Integrating  Equations  A. — 1st  Step. 

IST  STEP. — The  first  step  in  the  process  of  integration  is 
to  replace  R  by  its  value  from  equation  (263), 


and  to  make 

/(*>)  =  *r, (277) 

in  which  n  represents  the, exponent  of  the  power  of  v  which 
is  proportional  to  the  retardation,  for  any  particular  velocity, 
and,  according  to  Mayevski's  experiments  as  shown,  varies 
from  2  to  6. 

From  equation  (269)  we  have 

vl  =  v  cos  6 ; 


EXTERIOR   BALLISTICS. 


359 


hence 


Making  these  substitutions  in  the  value  of  R  above,  we 
have 


A 


W~  C  cos  «  ff 


(279) 


Substituting   this  value  of  R  in   the   first,  second,  and 
fourth  of  equations  (A),  we  have 


C 
dt=~  A 

<**=-  — 


dv 


\\     •    •    •    •    (280) 


(281) 


(282) 


Dividing  both  terms  of  (282)  by  cos'  0,  we  have 

'    '    '   '   <** 


or,  since  cos  6  = 


sec  ff 

m 


gC         dv, 


cos2  e      A  sec""1  0v 
Collecting  these  equations,  we  have 


(284) 


dV 


A 


J_C_         dv,    . 

3?^ecM  ~ x  6  v?  ' 
C         dv, 


•     (285) 


360  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

202.  Method  of  Integration  of  Equations  (A)— 2d  Step. 

2D  STEP.— In  equations  (285),  deduced  by  the  ist  step, 
the  first  members  are  exact  integrals.  The  second  members 
are  not,  however,  because  they  contain  the  two  independent 
variables  see""1  0  and  vr  For  all  cases  of  direct  fire  the 
value  of  sec  0  differs  but  little  from  unity,  since  for  angles 
of  15°,  sec  6  —  1.035,  and  for  angles  less  than  this,  its  value  is 
still  more  nearly  unity.  Hence  sec  6  can  be  replaced  by 
unity  without  great  error. 

Siacci  shows,  however,  by  analysis,  that  a  more  correct 
value  for  direct  fire  is 

sec*  -  '  0  =  sec"  - 2  0, (286) 

and  this  value  has  been  universally  adopted. 

Substituting  this  value  of  sec"  ~ I  0  in  equations  (285),  we 
have 

dB  gC  dv, 


cos2  0      A  sec*  ~2  0  v?  + * ' 
C          dv, 


dt=  - 


A  sec*  ~ 2  0  I'/   : 


.  C  dv, 

dx  =  — 


A  sec*  ~ 2  0  vf  ~ x" 


.     .     .    (287) 


Taking  the  first  of  equations  (287),  multiply  the  numer- 
ator and  denominator  of  the  second  member  by  sec3  0  = 
sec2  0  sec  0,  and  we  have 


cos3  6    ~  A 

Butsec20  = 5-z»   and   since   0  is  constant,  sec  0  dvl  = 

d(y^  sec  0);  hence 

dti  gCd(i\  sec  0) 

cos2  6  ~~  A  cos"  0  (v,  sec  0)*  + r  ' 

and  by  the  same  process  the  other  two  equations  may  be 
placed  in  a  form  in  which  the  second  members  can  readily 
be  integrated.  Hence  we  have 


EXTERIOR  BALLISTICS. 

dO  gC         d(v^  sec  0) 


cos2  0       A  cos2  0  (^  sec  0)w 


^4  cos  0  (vl  sec  0) 

C    d(y^  sec  0) 
~ 


,  sec 


361 


(288) 


Making 


v,  sec  0  = 


^  cos  6 
cos  0 


F  cos  0 

F,  sec  0  =  —  — T-  =  F, 
cos  0 


(289) 

(290) 


from  equation  (269),  and  integrating  equations  (288)  between 
the  limits  0  and  6  to  which  correspond  Fand  u,  we  have 


tan  0  -  tan  6  =  n  /^  0[j,  -  ^];      .     (291) 

7-WT-x    ;     •     •     (292) 


/  = 


#  = 


C 

(n  —  i)^4  cos  0L&' 

(Jt^t^^wrrrl (293) 


203.  Simplification  of  Equations  (291),  (292),  and  (293)— Method 

of  Calculating  the  Functions  which  Enter  them. 
SIMPLIFICATION. — To  simplify  equations  (291),  (292),  and 
(293),  make 


/(«)  = 


(294) 


T-(«)  = 


.  .  .   (295) 
.   .  .  (296) 


s(«0  = 


>-2)^» 


-+Q' 


.    (297) 


362  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

Making   these   substitutions,  equations  (291),  (292),  and 
(293)  can  be  written, 

.    (B) 


'  See  (289)  ......    '    '    '    (F) 

In  equations  (294),  (295),  etc.,  the  expression  /(«),  is 
called  the  inclination  function,  T  (u)  the  time  function,  and 
S(u)  the  space  function;  Q,  Q\  Q";,  etc.,  are  arbitrary  con- 
stants. The  values  of  these  iunctions  may  be  calculated 
and  tabulated  for  convenience,  and  the  resulting  tables  are 
called  "  Ballistic  Tables."  Those  used  in  the  present  course 
were  calculated  by  Capt.  James  M.  Ingalls,  ist  Artillery, 
U.  S.  Army.  By  their  use  the  calculation  of  these  functions 
is  avoided  for  any  particular  case,  and  the  use  of  the  formu- 
las facilitated. 

CALCULATION  OF  FUNCTIONS.  —  As  an  illustration  of  the 
method  of  calculation,  take  the  T(u)  function,  equation  (296): 


In  this  equation,  n  is  the  exponent  of  the  power  of  v  to 
which  the  resistance  of  the  air  is  proportional  ;  A,  a  constant 
determined  by  Mayevski's  experiments,  as  explained  ;  and 
Q"  an  arbitrary  constant. 

For  values  of  v  greater  than  1330  ft.-secs.,  we  have  n  —  2 
and  log  A  —  4.1525284.  Hence  for  these  velocities  we  have 

T(u)  =  -^-^  -  +  Q". 
[4.1525284]  « 

The  ballistic  tables  are  so  constructed  that  all  the  func- 


EXTERIOR  BALLISTICS.  363 

tions  S(u),  T(u),  etc.,  reduce  to  zero  for  u  =  2800  ft.-secs. 
Hence  we  have 


and  solving 

<2"=:-  2.5137. 

When    the    velocity  is    1330   ft.-secs.,  n  —  3  ;    log  A  = 
7.0364351  ;  hence 


T(u}  = 


2  x  [7.036435 


But  to  avoid  abrupt  changes  in  the  table,  the  value  of 
T(u)  for  1330  ft.-secs.  must  be  placed  equal  to  that  which 
would  be  obtained  if  n  =  2,  or  from  the  first  equation  in 
which  Q"  enters.  This  may  be  done,  since  Q"  is  arbitrary, 
by  placing 


-2.5137= 


[4.1525284]  x  1330  2  x  [7-0364351]  x  1330 

Solving  with  reference  to  g/',  we  have 
£"  =  +0.1791. 

Therefore,  for  all  values  of  u  or  v  greater  than  1330  ft.- 
secs.  the  value  of  T(u)  is  calculated  by  the  equation 


[4,525284]  x« 

and  for  all  values  of  u  or  v  between  1330  and   1120  ft.-secs. 
by  the  equation 

T(u)  =  -  =  -  +  0.1701. 
2  X  [7.036435  i]X«' 

Below  1  1  20  ft.-secs.  we  make  a  similar  change,  equating 
the  known  value  for  1120  with  the  new  values  for  A  and  », 
and  determine  the  new  arbitrary  constant  as  before,  and  so 
on  for  all  the  functions. 


364  TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 

204.  Relation  between  x  and  y. 

We  have  from  equation  (B),  since  tan  6  =  -~t 

dy  C 

/-  =  tan  0  - 


2  COS*  0 


also, 

fc/j  =  v  COS  0 

z>  cos  B 
Vl  Sec  *  =  cos  0   =  *  (See      9^' 

d  (z/j  sec  0)  =  d#. 

Whence,  substituting  in  the  third  ol  equations  (288),  we 
have 

C    du 
~  A  u«~* 
or 

dx  du 

.......    (299) 


Multiplying  (299)  and  (298)  together  member  by  member, 
we  have 


2  COS'    .     ,     . 

—  tan 


6T2 

Integrating  and  making  x  and  y  both  zero  at  the  origin, 
where  u '=  F,  we  have 


C  AJu     w 

Making 


we  have 
2  cos2  0 


EXTERIOR  BALLISTICS,  365 

From  equation  (D)  we  have 

?L  =  S(u)  —  S(V) (301) 

Dividing  (300)  by  (301),  member  by  member,  we  have 


Au—A 

(302) 


or  finally, 

y  C       \A(u)-A(V) 

x  --.  tan  0  -    2  cog2  ^  |  s^  —'S(r)  ' 

In  this  equation  A  (21}  is  called  the  altitude  function. 
Collecting  these  equations,  we  write 


.     .     .     (B) 


(C) 
cos 


(D) 


cos  6  /T_ 

u  —  v-—- (F) 

COS0 

These  are  the  fundamental  equations  of  Exterior  Ballis- 
tics, and  the  object  now  is  to  explain  their  modifications  and 
methods  of  use. 

205.  Modifications  of  General  Formulas  for  the  Whole  Range  X— 

For  the  Summit  of  the  Trajectory. 

MODIFICATIONS  FOR  RANGE  X. — The  range  being  the 
distance  from  the  muzzle,  to  the  point  where  the  projectile 
in  the  descending  branch  of  the  trajectory,  pierces  the  hori- 
zontal plane  through  the  muzzle,  we  have  for  this  point 

—  8  =  &)• 

t  =  T: 

u  =  u  <« 


366  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

and  making  these  changes  in  (B),  (C),  (D),  (E),  and  (F),  we 
have 


Combining  (B')  and  (Ex)  and  eliminating  /(F),  we  have 

Au»-A 


SUMMIT  OF  TRAJECTORY.— For  this  point  we  have  6  =  o, 
and  since 

sin  20  =  2  sin  0  cos  0, 
we  have  from  equation  (B) 


•  ...  (303) 

\^ 
and  from  (F) 

U'  =  ^' (3°4) 

in  which  u0  and  VQ  are  the  values  of  u  and  v  for  the  summit 
of  the  trajectory. 

Substituting  in  (Er)  for 


its  value  from  (303),  we  have 


EXTERIOR    BALLISTICS.  367 

and  this  value  in  (E')  and  (G)  gives 

sin  20-  cj/(*.)-/(F)]-;.    •  •    •    (306) 

tan  °° =  7(«")  -  7«> •      (307) 


When  0  and  GO  are  both  small,  as  in  direct  fire,  we  may 
without  material  error  suppose 

0  —  GO, 
hence 

2  cos a  0  tan  GO  =  2  cos 2  GO  tan  GO  =  sin  2co ; 

and  substituting  in  (307),  we  have 

sin  2Go  ~  £"•!  /(#«)  —  /(«0)  [  •       ...     (308) 

206.  Auxiliary  Formulas. 

Equations  (E),  (E7),  and  (G)  can  be  more  readily  used  for 
calculation,  if  the  quantities 

A(u)-A(V] 


and 

(*) 


are  calculated  and  tabulated  for  use. 

jf 

These  quantities  are  functions  of  -^  and    V,  as  may  be 

o 

shown  in  the  following  manner: 

Suppose  it  is  required  to  compute  the  height  of  trajec- 
tory y,  by  (E),  angle  0  by  (E'),  and  angle  K>  by  (G),  having 
given  the  ballistic  coefficient  C,  the  initial  velocity  F,  and 
the  whole  range  X,  or  part  of  the  range  x. 

In  equation  (E),  0  and  u  are  unknown.  0  can  be  com- 
puted from  (Ex)  when  (#w)  is  known,  and  GO  in  (G)  can  be 
computed  also  when  (uu)  is  known. 

Hence  (uu)  is  the  only  unknown  quantity  required  to 
complete  the  solution.  uu  can  be  found  from  (Dr),  since 


368  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

and  u  can  be  found  from  (D)  since 
? 

It  follows  from  this  that  the  quantities  (a)  and  (b)  are  func^ 

tions  of  -^,  or  ^  and  F,  and  therefore  the  values  of  these 
C-  o 

J£ 

expressions  when  tabulated  should  have  -=  and  V  as  argu- 

o 

ments. 

We  therefore  place 

A(u.)-A(V)      I(V, 
~  J^> 

- 

*''  •   •   •  (3IO) 


a  +  &     =m,    .     .     .     (313) 

and  making  the  corresponding  changes  in  equation  (B),  we 
have 

tan  6  =  tan  0  ---  r—  - 
2  cos'  0  * 

reducing 

tan0  =  tan0{i-i^r(.      .    .    .    (314) 
In  (E), 


^r  2  COS 

reducing 

(315) 


in  (E'), 

sin  20  =  AC,      .........     (31-6) 


EXTERIOR  BALLISTICS.  3691 

in  (G), 


and  for  small  angles  of  elevation,  since 

0  =  «, 
we  have,  from  (317), 

sin  200  =  BC.  .     .     .     .     .     .    (318) 

Substituting  in  (314)  and  (315)  for  sin  20  its  value  from 
(316),  we  have 

tan  0  =  tan  0  |  I  -  ^  j  ;    .     .     .     .     (319) 

.    .     .    (320) 

The  auxiliary  quantities  #,  £,  A,  B,  m,  are  generally 
written  a  —  f(zV\  b  =f(zV),  m  =f(zV\  etc. 

207.  Explanation  of  Ballistic  Tables. 

The  values  of  the  quantities  A  (u),  S(u),  T(u),  etc.,  have 
been  calculated  and  tabulated  as  before  explained,  and  their 
values  are  found  in  Ballistic  Table  I,  for  all  velocities  from 
2800  to  400  ft.-seconds,  for  ogfval  projectiles.  Table  II 
gives  the  value  of  the  corresponding  quantities  for  spherical 
projectiles. 

In  these  tables  u  is  a  general  expression  for  velocity, 
so  that  if  v  or  V  be  given,  its  value  will  be  found  in  the 
column  headed  u  in  the  tables. 

To  illustrate  their  use,  find  the  values  of  the  different 
functions  from  Table  I,  for  a  velocity  of  1137.6  ft.-secs. 

We  have  from  the  table 

S(u)  =  5(1137.6);  5(1137)  =6413-2; 

5(o.6)  =        4-26  =  7.1  X  .6  =  4.26. 
£(1137.6)  =  6408.9 

A(u)  =  A  (1137-6);  A  (i  137)  =  341-73  ; 

A  (0.6)  =        .636  =  i.  06  X  .6  =  .636. 

A  (1.37.6)  =  341-09 


37°  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

/(«)  =  /(!  137.6);  7(i  137)  =  0.14942 

7(o.6)  =  .000216  =  00036  X  .6  =.0002  1  6 
7(1137^))  =  0.14920 

T(u)=  ^(1137.6);  T(i  137)  =  3-736; 

r(o.6)  =  .0036  =  .006  X  .6  =  .0036 
=  3-732 


Conversely,  having  the  values  of  the  quantities  5  (u)y 
A(u),  etc.,  to  find  the  corresponding  values  of  «,  we  proceed 
as  follows  : 

Find  the  value  of  u  for 

S(u)  =6430.7; 
A(u)=    360.9  ; 
f(u)  =       0.1580; 
7»  =        3-720. 

From  Table  I  we  have 

5  («)  =  6427.4,    «  =  1135, 
6430.7  -  6427.4  =  3.3. 

Tabular  difference  for  i  ft.-sec.  =  7.2. 

7.2:3.3:11:* 
x  —  0.46  ft.-secs., 
hence 

u  for  S(#)  =  6430.7  =  1135  —  0.46  =  1134.54  ft.-secs.; 
A  (u)  =    360.45,    u  —  1120  ft.-secs.; 

360.9  -  360.45  =  0.45- 
Tabular  difference  for  i  ft-sec.  =  1.15. 
1.15  :o.45::  I  :*; 

x  —  0.39  ft.  -sees.; 
hence 

u  for  A  (u)  =  360.9  =  1  1  20  —  0.39  =  1119.61  ft.-secs. 


EXTERIOR   BALLISTICS.  371 

The  same  method  applies  to  all  other  cases,  and  it  is 
evident  that  the  table  is  used  like  a  table  of  logarithms. 

208.  Auxiliary  Tables— Values  of/(zF),  z,  and  V. 

These  tables  are  found  in  Ballistic  Table  I,  and  give  the 
values  of  the  quantities  A,  B,a,  b,  and  m  ;  and  the  tables  are 
headed  "  auxiliary  A,"  "auxiliary  B"  and  "auxiliary  m." 
The  values  of  a  and  b  are  taken  from  the  table  for  A  and  B, 
since  a  and  b  are  general  cases  of  A  and  B.  The  expressions 
for  these  quantities  are  given  by  equations  (309)  to  (313),  and 
their  values  were  calculated  and  tabulated  by  Capt.  Ingalls. 

By  referring  to  the  tables  it  will  be  seen  that  the  argu- 

x       X 

ments  are  z  and  v.     z  is  used  for  brevity  in  place  of  ~^  or  — , 

C         C 

and  hence  the  value  of  z  is 

x  X 

*=c  or  ~c (32I) 

In  this  table  there  are  two  columns  of  differences,  Az  and 

4* 

Az  corresponds  to  differences  in  the  argument  z,  and  Av  to 
those  of  the  argument  V. 

USE  OF  TABLES. — We  may  have  the  following  cases  : 

1.  A  given  value  of  z  and  one  of  F,  neither  of  which  is 
found  in  the  table ;  to  find  the  corresponding  value  of  A,  B, 
or  m. 

2.  A  given  value  of  A,  B,  or  m  and  one  of  V,  neither  of 
which  is  found  in  the  table  ;  to  find  the  corresponding  value 
of*. 

3.  A  given  value  of  A,  B,  or  m,  and  one  of  z,  neither  of 
which  is  found  in  the  table ;  to  find  the  corresponding  value 
of  F. 

Suppose  we  have  a  value  of  z  and  one  of  F  given,  and 
the  corresponding  value  of  A,  B,  or  m  is  required. 
Let/^F)  denote  the  value  sought ; 

zt  and  F0  the  next  smaller  values  of  z  and  F  found  in 

the  tables ; 
/  G&o  F0)  the  value  from  table  corresponding  to  z0  and 


372  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

For  an  increase  of  100  in  z,  we  find  that/(#eF0)  increases 
by  4,  ;    hence,  for  an  increase  of  z  —  z0  ,  the  increase   in 

f(*.V.)  will  be 

loo  :  z  —  z9  :  :  Ax  :  x  ; 


x  — 


100 


Again,  for  an  increase  of  50  ft.-secs.  in  F,  /(#,  F0)  decreases 
by  dv  ;  hence,  following  the  same  rule,  the  decrease  for 
F-  F0  will  be 

F  —  F 


The  true  value  of  /(sF)  then  will  be 

A  =/(,F)  =/(..F.)  +  A-          ^  A.     (322) 


Suppose  now  we  have  given  f(zV)  and  F,  and  wish  to 
find  z. 

Solving  equation  (322)  for  z,  we  have 

inn   (  F—  F 


Or,  having  f(zV)  and  ^,  required  F.     Solving  equation 
(322)  for  F,  we  have 


--  (324) 


209.  Examples  of  Use  of  Auxiliary  Tables—  Ballistic  Coefficient—  -^. 

EXAMPLE  i.  Find  the  value  of  A  =zf(zV)  for  z  =  1446.7 
and  V  —  1224.4. 

In  formula  (322)  we  have 

z.  =  1400  ; 

F0  =  1200; 


Az  =  .0028  ; 
4,  =  .0025  ; 

*  —  z.  =  46.7  ; 


EXTERIOR  BALLISTICS.  373 

Hence 


4.6.7  . 

A  =  f(*V)  =  .0352  +         X  .0028  -  -       X  .0025, 


f(zV)  =  .0352  +  .0000876  =  .0353. 

In  a  similar  manner  B  =  f(zV),  and  m=f(zV)  may  be 
found  by  using  the  proper  tables. 

EXAMPLE  2.  Find  z  for  B  =f(zV)  =  0.1430,  and  V—  1740. 
In  formula  (323)  we  have 

z0  for  F(i70o)  and  B  (.1409)  =  5100. 

4,  =  .0046  ; 

4,  =  .0054  ; 
F-  F0  =  4o; 
f(*r)  =  0.1430; 
/(*.Fi)  =  0.1409; 

F0  =  1700. 

Hence 


In  a  similar  manner,  having  f(zV)  =  A  or  m,  z  may  be 
found,  using  the  proper  tables. 

EXAMPLE  3.  Find  V  for  m  —  f(zV)  —  0.2400  and  z  =  5250. 
In  formula  (324)  we  have 

V.  for  m  (.2331)  and  z0  (5200)  =  1750, 

Av  —  .0101  ; 
4,  =  .0072  ; 

*  —  ^o  =  5o  ; 


jar.  =  5200  ; 

/(^r)  =  .24oo. 

Hence 
V=  '75°  +  ^i  {  £  X  .0072  +  -2331  -  -2400 

v=  1733-67- 


374  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

In  a  similar  manner,  having  f(zV)  =  A  or  B,  V  may  be 
found,  using  the  proper  tables. 

BALLISTIC  COEFFICIENT.  —  The  value  of  this  coefficient 
is  given  by  equation  (264),  and  its  calculation  involves  that 


ft  ft 

CALCULATION  OF  -p  —  The  values  of  ^  are  given  in  Table 

III,  for  degrees  Fahrenheit  from  o°  to  100°,  and  for  heights 

ft 

of  barometer  from  28  to  31  inches.      To  find  the  value  of  ~ 

for  any  intermediate  values  of  F  and  H  not  in  the  tables,  we 

proceed  exactly  as  in  the  case  of  the  auxiliary  tables. 

ft 

EXAMPLE.  —  Find  the  value  of  -r1  for  F  =  49°.  6  and  H  =.- 

29.30  inches.     From  Table  III  we  have 

s^ 
For  F  =  49°  and  H  =  29  inches  ;  ^  =  1.0,12  ; 

t\ 
Difference  —  for  i°  F=  +  .002  ; 

Difference  for  o°.6  =  +  .0012; 

p. 
Difference  ~  for  i  inch  H  —  —  .034  ; 

Difference  for  0.30  inch  —  —  .0102. 
Hence 

-^  for  F=  49°  .6  and  H—  29.  30  inches  =:  1.012  -}-  .0012  —  .0102 

=  1-003. 


PRACTICAL  PROBLEMS. 

210.  Kind  of  Fire  to  which  Formulas  Apply—  Problem  I—  Use  of 

Equation  B. 

KIND  OF  FIRE.  —  The  formulas  above  deduced  apply 
strictly  to  direct  fire  only,  where  the  values  of  0  and  6  are 
so  small  that  Siacci's  value  of  sec  0  may  be  used  without 
appreciable  error. 


EXTERIOR   BALLISTICS. 


375 


The  formulas  give,  however,  sufficiently  accurate  results 
for  indirect  or  curved  fire,  and  hence  they  are  used  for  both 
direct  and  curved  fire ;  but  for  mortar  fire  they  must  be 
modified,  as  will  be  explained. 

PROBLEM  I  —  USE  OF  EQUATION  (D).  —  Assume  equa- 
tion (D), 

*  =  C\S(u)-S(V)-\. 

Since  C  is  generally  known,  we  have  in  this  equation 
three  quantities,  xy  u,  and  V,  any  two  of  which  being  given, 
the  third  can  be  found.  Solving  equation  (D)  for  each  of 
the  three  quantities,  we  can  write 


or,  since 


the  two  latter  can  be  written 


For  the  whole  range  X  we  have  similar  equations, 
changing  u  into  UM  and  x  into  X.  Collecting  these  equa- 
tions, we  have 

x=C[S(u)-S(V)-\; 


•    •    (325) 


S(r)=S(u)-*; 

X=C\_S(u»)-S(V}}; 


x      X 


376 


TEXT-BOOK  OF  ORDNANCE  AND   GUNNERY. 


These  equations  enable  us  to  solve  the  following  prob- 
lems, which  may  be  grouped  under  Problem  i. 


Given. 

Required. 

C,u,  V 

X 

C,  V,x 

U 

C,  x,  u 

V 

C,  u.,  V 

X 

C,  V,X 

u*> 

C,  X,  uu 

V 

In  this  problem,  if  the  angle  of  elevation  does  not  exceed 
10°,  the  values  of  u  and  v  will  be  practically  the  same,  but 
for  angles  greater  than  10°  the  value  of  t/must  be  calculated 
from  that  of  u  by  equation  (F), 

cos  0 
*cos7' 

and  tor  this  purpose  the  value  of  6  must  be  known. 
Its  calculation  will  be  explained  later. 

Problem  2.— Use  of  Equations  (316)  and  (321). 
Assuming  the  above  equations,  we  have 

sin  20  =  A  C:    . 


(316) 
(321) 


i.  Having  C,  0,  and  V,  find  the  whole  range  X. 
From  (321)  we  have 

X=Cs. 

In  this  equation  X  and  z  are  unknown. 
But  A  =f(zV\  and  from  (316) 


Hence  in  the  equation  A  =  f(zV\  we  have/(^F)  and  V 
given  to  find  z,  which  is  obtained  from  equation  (323),  using 
auxiliary  table  A. 

This  value  in  equation  (321)  will  give  X. 


EXTERIOR   BALLISTICS. 


377 


2.  Having  C,  0,  and  X,  find  the  initial  velocity  F.     We 
have 

A=f(zV\ 

in  which  A,  z,  and  Fare  unknown.     But  from  (316) 

sin  20 


and  from  (321) 


X 
*=> 


Hence  we  have  f(zV)  and  z  given  to  find  F,  which  is 
obtained  from  formula  (324),  using  auxiliary  table  A. 

3.  Having  C,  F,  and  X,  find  the  angle  of  elevation  0. 

From  (316)  we  have 

sin  20  =  AC, 
in  which  A  and  0  are  unknown.     But 

in  which 

X 
2=^ 

and  F  is  given.     Hence  we  can  find  A  by  formula  (322), 
using  auxiliary  table  A.     This  value  of  A  in  (316)  gives  0. 
We  have,  therefore,  for  Problem  2, 


Given. 

Required. 

C,  4>,  V 

X 

c,<t>,x 
c,  v,x 

V 

0 

212.  Problem  3 — Time  of  Flight. 

i.  Having  C,  0,  F,  and  x,  find  the  time  of  flight  for  the 
range  x. 

From  equation  (C)  we  have 

C    [T(u-(T(V)l 


COS  0 


in  which  «,  the  velocity  at  the  point  x,  and  t,  the  time  to 
that  point,  are  unknown. 


37$  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

But  we  have,  equation  (D), 


in  which  z  =  -~  and  F  are  known.     Hence  u  can  be  deter- 
mined, and  this  value  of  u  in  equation  (C)  will  give  t. 
If  0  =  or  <  10°,  u  —  v ;  if  0  >  10°, 

COS0 

cos  0' 

2.  Having  C,  0,  F,  and  X,  find  the  time  of  flight  for  the 
whole  range  X. 

From  equation  (C')  we  have 


cos  0 

in  which  «w,  the  remaining  velocity  at  the  end  of  the  range, 
and  T,  the  time  to  that  point,  are  unknown. 
But  we  have,  equation  (D'), 


in  which  z  =-^  and  Fare  known.     Hence  uu  can  be  deter- 
o 

mined,  and  this  value  of  UM  in  equation  (C;)  will  give  T. 
The  same  remarks  apply  to  u  and  Fas  in  i. 
If  0  =  or  <  5°,  cos  0=i,  practically,  and  we  have 


For  Problem  3  we  have,  then, 


Given. 

Required. 

C,  </>,  V,  x 
C,  <1>,  V,  X 

t 

T 

213.  Problem  4 — Angle  of  Inclination. 

i.  Having  C,  0,  F,  and  ^r,  find  the  value  of  0,  the  inclina- 
tion of  the  tangent  at  the  point  x. 


EXTERIOR  BALLISTICS.  379 

We  have,  irom  (314), 


in  which  0  and  m  are  unknown.     We  have 

m=f(*V\ 
in  which  m  and  2  are  unknown.     But  from  (321) 


from  which  z  can  be  found,  and  hence  m  by  formula  (322),. 
using  auxiliary  table  m. 

This  value  of  m  in  (314)  will  give  9.  The  value  of  6  thus 
found,  when  substituted  in  equation  (F),  will  give  v  when- 
ever 0  >  10°. 

The  value  of  6  may  also  be  calculated  from  equation 

(319), 

r     «~i 

tan  6  =  tan  0  I  i  —  -jj, 
in  which  m  is  found  as  above,  and 

A  =  ™^*-    (equation  (316)). 

2.  Having  £,  0,  F,  and  ^T,  find  the  value  of  <»,  the  angle 
of  fall. 

We  have  from  (317) 

BC 

tan  GO  =  -  5—  -  , 
2  cos2  0* 

in  which  /?  and  GO  are  unknown.     But  we  have 


in  which  B  and  #  are  unknown.     From  (321) 

X 

*  =  T' 

from  which  £  can  be  found.     We  have  then  z  and  F  given, 


380  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

from  which  B  =f(zV)  can  be  found,  using  auxiliary  table  B 
and  formula  (322),  and  this  value  of  B  in  (317)  will  give  GO. 
If  0  =  or  <  5°,  we  have,  equation  (318), 

sin  2ao  =  B  C. 

214.  Problem  5 — Height  of  Trajectory — Maximum  Height. 

HEIGHT  OF  TRAJECTORY. — Having  Cy  0,  V,  and  x,  find 
the  height  of  the  trajectory  at  the  range  x. 

We  have  from  (320) 

r—  —i 

y  =  x  tan  0     i  —  -  -    , 

l_  *L I 

in  which  y,  a,  and  A  are  unknown.     From  (316)  we  have 

_  sin  20 
A  —       ~^> — , 

from  which  A  can  be  determined.     We  have  also 

in  which  a  and  z  are  unknown.     But 

x 

'=?> 

from  which  z  can  be  determined,  and  we  have  then  z  and  V 
given,  from  which  we  can  find  a—f(zV)  by  the  use  of  aux- 
iliary table  Ay  and  formula  (322).  These  values  of  A  and  a 
in  (320)  will  give  y.  Equation  (315)  may  also  be  used. 

MAXIMUM  HEIGHT.  —  Having  C,  0,  and  V,  find  the 
maximum  height  of  the  trajectory. 

This  will  be  at  the  summit  of  the  trajectory,  and  for  this 
point  6  —  o. 

We  have  from  (320) 


in  which  y,  x,  a,  and  A  are  unknown. 

For  the  summit  of  the  trajectory  make  y  =  y»  and  x  = 

To  find  #0,  we  have,  (321), 

x,  =  Cz, 
in  which  #0and  z  are  unknown.    Assume  equation  (319), 


tan  6  =  tan  0  [i  —  Sfl 


EXTERIOR   BALLISTICS.  381 

Since  Q  =  o  at  the  summit,  we  have 

m  —A, 
and  from  (316) 

sin  20 
m  =  A  =  —  gr—  ,    .....     (326) 

from  which  m  can  be   determined.     Then  m-=.f(zV\  in 
which  m  and  V  are  known  and  z  can  be  found  by  auxiliary 
table  m  and  formula  (322).     This  value  of  z  in  (321)  above 
will  give  x0,  the  range  corresponding  to  the  summit. 
In  equation  (320),  since  m  =  A  by  (326),  we  have 


but 

m  =  a  +  b. 
Hence 

ra  +  6-a] 
,.  =  *..  tan  *L—  —  J> 

or 

£ 
^  =  *0  tan  0  —  ......    (327) 

In  this  equation  y^  and  b  are  unknown.  But  we  have 
b=f(zV\  in  which  z  and  Fare  known,  and  hence  b  can  be 
calculated  by  auxiliary  table  B  and  formula  (322).  This 
value  in  (327)  will  give  _^0. 

215.  Problem  6  —  To  Determine   the  Dangerous  Space  —  Rule  of 

Double  Position. 

DANGEROUS  SPACE.  —  The  dangerous  space  is  the  hori- 
zontal distance  over  which  an  object  of  a  given  height  will 
be  struck.  Suppose  the  height  of  the  object  is.  6  feet.  If 
we  find  first  the  whole  range  f<gr  a  given  elevation,  initial 
velocity,  etc.,  and  then  find  the  range  at  which  the  height 
of  the  trajectory  is  6  feet,  it  is  evident  that  for  every  point 
beyond  this  latter  range,  in  the  descending  branch  of  the 
trajectory,  the  height  will  be  less  than  6  feet,  and  the  object 
will  be  struck.  The  dangerous  space,  then,  is  the  difference 
between  the  whole  range,  and  the  range  corresponding  to  the 
given  height.  It  is  also  evident  that  in  general  there  will 
be  two  points  of  the  trajectory  whose  heights  are  the  same 


$82  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

— one  point  in  the  ascending  branch,  and  one  in  the  descend- 
ing branch.  The  point  in  the  descending  branch  is  alone 
considered. 

The  problem  then  resolves  itself  into  computing  first  the 
whole  range,  and  then  the  range  whose  ordinate  is  y,  and 
taking  their  difference. 

DATA. — The  data  are  C,  0,  and  V. 

METHOD. — To  find  the  whole  range  X,  use  the  method 
of  Problem  2. 

To  find  the  abscissa  of  the  point  whose  ordinate  is  y. 
This  problem  is  apparently  the  inverse  of  Problem  5,  for 
which  equation  (320)  is  used  ;  but  on  examining  that  equa- 
tion it  will  be  found  that  a  is  a  function  of  ;r,  and  hence  we 
have  two  unknown  quantities,  and  the  equation  cannot  be 
solved.  The  same  is  true  of  all  the  equations  into  which  y 
and  x  enter ;  there  is  no  direct  and  simple  relation  between 
them.  Hence  the  problem  must  be  solved  by  approxima- 
tion. 

For  this  purpose  combine  equations  (D),  (E),  and  (303), 
and  we  have 


/(*.)  S(u)-A  (u)  =  —~y  +  I(u.)S(r)  -  A  (V).  (328) 

In  this  equation  we  can  compute  /(«„)  by  (303),  and  hence 
all  the  quantities  which  enter  the  second  member  are 
known. 

Represent  this  known  quantity  by  k.     Then  we  have 

k  =  I(u0}S(u)-A(u), 

in  which  u0  is  known,  and  we  have  to  determine  the  value 
of  u  by  approximation. 

RULE  OF  "  DOUBLE  POSITION."— For  this  purpose  we 
make  use  ot  a  method  called  the  rule  of  "  double  position." 
Suppose  we  have  an  unknown  quantity  u  whose  value  is 
sought.  Let  #!  represent  a  quantity  slightly  greater  than  u, 
and  &,  a  quantity  slightly  smaller. 

Suppose  u^  substituted  for  u  in  the  given  equation,  and 
the  latter  solved.  A  certain  value  will  be  obtained  which 
will  be  erroneous.  Denote  the  difference  between  this 
erroneous  value  and  the  true  value  by  et.  Similarly,  sub- 


EXTERIOR  BALLISTICS.  383 

stitute  u^  for  u,  and  denote  the  difference  between  the 
erroneous  value  and  the  true  value  by  ea. 

Then  the  hypothesis  upon  which  the  rule  of  double  posi- 
tion is  based  is,  that  the  errors  el  and  ea  in  the  results  are 
proportional  to  the  errors  made  in  assuming  the  values  of  «, 
and  «2. 

The  errors  in  assuming  ul  and  #a  are 


and 

u  —  u,\ 

and  from  the  above  hypothesis  we  have 

e,  :  ea  ::  u  -  «,  :  u  —  «a, 
and  by  division 

fci  —  ea  :  ea  ::  #2  —  ^  :  «  —  #a; 

€,  —  e,  :  e,  ::  «a  —  «t  :  *  —  «t, 

which  expresses  the  rule  of  "  Double  Position." 

216.  Example. 

The  above  is  best  illustrated  by  a  numerical  example. 
Suppose  k  =  17666.1,  and  /(#„)  =  1.55658. 
Then  we  have 

17666.1  =  1.55658  S(u)  —  A  (u). 
Suppose 

u,  =  430  ft.-secs.; 

5(^  =  21579.4; 
A(u)=  15797.3; 

17666.1  =  1.55658  x  21579.4  -  15797-3; 

€1  =  +  126.6. 

Again,  suppose 

u^  =  420  ft.-secs.  ; 

5  («)  =  21978.7; 
A  (*)=  16861.3; 

17666.1  =  1.55658  X  21978.7  —  16861.3; 
e,  =  -  315.9; 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 
£,  -  €,  =  126.6  -f  315.9  =  442.5  ; 

*,=  -  SIS-?; 
U9  —  Ut  =  -  10  ; 

u  —  #a  =  u  —  420. 
Then 

442.5  :  —  315.9  ::  —  10  :  u  —  420. 

u  —  427.139  ft.-secs. 

This  value  of  u  in  the  equation  containing  S(u)  and  A  (u) 
gives 

e,  =  +6.6. 

It  is  necessary  therefore  to  make  a  second  trial.    Assum- 
ing u9  =  426.8  ft.-secs.,  and  proceeding  as  before,  we  find 

e,  =  -  8.2  ; 
and  forming  the  same  proportion  as  before,  we  find 

u  =  426.9878  ft.-secs., 

and  this  value  of  u  will  satisfy  the  original  equation.  There 
is  also  another  value  of  u  which  will  satisfy  the  equation, 
but  it  will  readily  be  seen  that  it  belongs  to  the  ascending 
branch  of  the  trajectory,  and  is  not  used. 

Having  the  value  of  u  for  the  point  whose  ordinate  is  y 
we  find  x  by  equation  (D), 


and  the  dangerous  space  is 

S  =  X-  x. 

As  an  approximate  value  for  u  in  making  these  supposi- 
tions, the  value  u<*  for  the  end  of  the  range  may  be  calcu- 

lated and  used. 

\ 

217.  Eigidity  of  Trajectory—  Drift. 

RIGIDITY  OF  TRAJECTORY.  —  In  the  previous  problems  it 
has  been  assumed  that  the  point  of  fall  of  the  projectile  is 
in  the  horizontal  plane  passing  through  the  centre  of  the 
muzzle,  or  that  the  right  line  drawn  from  the  centre  of 
the  muzzle  to  the  end  of  the  range,  or  the  chord  of  the 
trajectory,  is  horizontal. 


EXTERIOR   BALLISTICS.  385 

Suppose,  however,  as  is  generally  the  case  in  practice, 
that  the  object  aimed  at  is  above  or  below  the  level  of  the 
gun,  the  angle  of  elevation  or  depression  being  a. 

Then  it  has  been  proved  analytically  that  the  relations 
existing  between  the  elements  of  the  trajectory,  and  the 
chord  which  represents  the  extreme  range,  are  the  same 
within  certain  limits,  whether  the  chord  is  horizontal  or  in- 
clined. In  other  words,  the  whole  trajectory,  with  its  chord, 
may  be  revolved  a  certain  distance  about  a  horizontal  axis 
passing  through  the  centre  of  the  muzzle,  without  changing 
the  relations  between  the  trajectory  and  its  chord. 

This  principle  is  called  the"  Rigidity  of  the  Trajectory," 
and  its  practical  use  is  as  follows  : 

Suppose  we  fire  at  an  object  whose  elevation  is  OL.  Cal- 
culate the  angle  of  elevation  0  for  the  given  range,  as  usual, 
and  aim  directly  at  the  target  with  the  rear  sight  set  at  the 
elevation  0.  The  act  of  aiming  at  the  target  gives  the 
actual  elevation  (0  -|-  a).  ,  If  a  is  depression,  it  is  affected 
with  a  minus  sign.  This  subject  is  discussed  later. 

DRIFT.  —  Mayevski's  formula  for  drift  is  (see  IngahV 
Hand-book) 


__ 
n     t  cos       1  S  («)  -  5  (V)  ~     *  (  K)  )  10,000  '     (329) 

in  which 

D  is  the  drift  in  feet  ; 

u  =  0.53  for  cored  shot  ; 

u  =  0.64  for  shell  ; 

n  =  the  twist  of  the  rifling  in  calibres,  at  the  muzzle 

-  =  0.41  for  projectiles  2.5  calibres  long  ; 
—  =  0.37  for  projectiles  2.8  calibres  long  ; 

-  —  0.32  for  projectiles  3.4  calibres  long  ; 

TT=  3.1416; 

g  =  32.2  feet  ; 

C,  0,  and  Fas  in  other  ballistic  problems  ; 


TEXT- BOOK   OF  ORDNANCE  AND    GUNNERY. 

B(u),  B(V],  M(V)  are  drift  functions  whose  values  are 
found  from  Table  I,  like  those  of  S(u),  A  («),  etc.; 
X,  the  range  in  feet. 

The  drift  will  be  more  or  less  affected  by  the  wind,  ac- 
cording to  its  direction  and  velocity,  and  its  effects  will  be 
further  explained  under  the  subject  of  Pointing. 

218.  Problem  7 — Mortar  Fire— Modified  Equations— Calculation. 

MODIFIED  EQUATIONS. — The  formulas  for  direct  fire 
were  obtained  from  the  differential  equations  (A)  by  assum- 
ing that  the  inclination  6,  of  the  tangent,  at  every  point  of 
the  trajectory,  is  relatively  small,  and  hence  its  cosine  or 
secant  constant,  and  approximately  unity.  For  high  angle 
or  mortar  fire,  however,  such  an  assumption  is  manifestly 
incorrect,  since  the  angle  6  varies  greatly  throughout  the 
trajectory. 

For  mortar  fire,  therefore,  Siacci  assumes  that  there 
is  a  mean  value  of  coo  0,  which  will  satisfy  the  differential 
equations,  and  make  their  second  members  exact  inte- 
grals. This  mean  value  is  denoted  by  a,  and  its  value  is 

shown  analytically  to  be  a  =  -  \  '     ,  (0)  representing 

tan  0  —  tan  u 

— ,  and  0,    I  r^—r,  and   their   numerical  values 

COS-+1  0  J    COS-+1  6* 

being  given  in  Table  IV,  together  with  the  values  of  tan 
4>  and  tan  0. 

This  is  applied  as  follows :  In  the  integration  of  equa- 
tions (A)  in  the  case  of  direct  fire,  the  second  step  consisted 
{see  page  360)  in  substituting  for  sec*-1  0,  the  constant  value 
secw~2  0.  But  for  mortar  fire,  a  must  be  substituted  for 
sec""1  0,  wherever  the  latter  occurs,  instead  of  sec"~2  0. 

To  show  the  effect  of  this  substitution,  take  the  second 

of  equations  (285),  dt  —  —  -j—     —j—n  —•     Writing  for  sec  0 

*cl   SeC  '     t\n 

its  mean  value  a,  we  have  dt  = - — \      Multiplying- 

Aan~l  vf 

numerator  and  denominator  by  a,  dt  = ~ — -L.      Repre- 

A    frf* 


EXTERIOR  BALLISTICS.  387 

senting  av^  by  u,  we  have  u  =  av1  =  av  cos  0.  Making  the 
same  substitutions  in  the  remaining  equations  (285),  and 
integrating,  we  have  the  following  formulas  for  mortar  fire  : 

....     (330) 
.    .    .    .    (331) 

....     (332) 


••     (333, 

in  which  5  is  the  length  of  any  arc  of  the  trajectory,  meas- 
ured from  the  origin  ;  U—  Va  cos  0  ;  u  =  av  cos  B  ;  v  = 
velocity  at  the  point  S;  6  =  the  inclination  of  the  tangent 
at  the  same  point. 

The  values  of  the  functions  A(u),  S(u),  etc.,  can  be  taken 
from  Table  I,  u  and  U  being  first  calculated  as  explained  in 
the  nomenclature. 

CALCULATION.  —  The  most  important  problems  in  mortar 
fire  are  to  find  the  whole  range  X,  and  the  time  of  flight,  T, 
for  that  range.  For  this  purpose  the  given  data  are  gen- 
erally C,  0,  and  V.  It  is  evident,  however,  that  with  the 
given  data,  equations  (331)  and  (332)  cannot  be  solved,  and 
the  solution  is  obtained  as  follows  : 

For  the  end  of  the  range  y  =  o,  and  from  equation  (333) 
we  have  , 


2  tan  0  >4K)  .       . 

~~  -         -  •  •   (334) 


For  mortar  fire  the  angle  of  fall  is  very  nearly  equal  to  the 
angle  of  elevation,  and  under  this  supposition  we  have, 
since  —  8  =  GO, 

(0)  -  (O)  (0)  +  (a?)  (0) 

tan  0  —  tan  0      tan  0  +  tan  GO       tan  0' 

from  which  a  is  known.  The  first  member  of  equation  (334) 
is  therefore  known,  and  also  A(U)  and  S(U)  in  the  second 
member.  u<*  is  therefore  found  by  "  Double  Position,"  as 
previously  explained.  This  value  of  um  in  (330),  (331),  and 
(332)  will  give  the  remaining  values  sought. 


388  TEXT-BOOK   Of    ORDNANCE  AND    GUNNERY. 

SUMMARY    TABLE. 


Given. 

Required. 

Problem. 

C,u,  V 

X 

I 

C,  V,x 

U 

I 

C,  x,  u 

V 

I 

C,  «M,  F 

X 

I 

C,  F,  X 

«» 

I 

X"1        \7~ 

C,  A,  HU 

V 

I 

C,  0,  F 

X 

2 

£  0,  ^ 

V 

2 

c,  v,x 

0 

2 

C,  0,  F,  x 

t 

3 

C,  0,  F,  ^ 

T 

3 

C,  0,  F,  * 

e 

4 

C,  0,  F,  ^ 

&) 

4 

£  0,  F,  * 

y 

5 

6",  0,  F 

y» 

5 

C,  0,  F 

*0 

5 

£  0,  V 

Dangerous  space 

6 

C,  0,  F 

X 

7 

(7,  0,  F 

X 

7 

C,  0,  F 

s 

7 

C,  0,  F 

t 

7 

£  0,  F 

T 

7 

C,  0,  F 

y 

7 

NOTE, — Ingalls'  Ballistic  Tables  are  to  be  used  in  these  problems,  and  the 
methods  of  Capt.  Ingalls  have  been  followed  in  deducing  the  equations. 


CHAPTER  VII. 

ARTILLERY    CARRIAGES— THEORY   OF   RECOIL. 

ARTILLERY   CARRIAGES. 

219.  Classification— Principal  Parts  of  Field  and  Siege   Gun  Car- 
riages— The  Axle. 

CLASSIFICATION. — Artillery  carriages  may  be  classified 
according  to  the  service  for  which  they  are  intended,  into 
field,  siege,  and  sea-coast  carriages. 

Field  and  siege  carriages  are  generally  wheeled,  and  are 
intended  to  support  the  guns  in  firing,  and  to  transport  them 
from  place  to  place,  with  their  ammunition  and  necessary 
supplies. 

Sea-coast  carriages  are  intended  only  to  support  the 
guns  in  firing,  and  hence  their  construction  differs  materi- 
ally from  that  of  field  and  siege  carriages. 

PRINCIPAL  PARTS  OF  FIELD  AND  SIEGE  GUN  CAR- 
RIAGES.— In  the  field  and  siege  services,  the  carriage  which 
supports  the  piece,  and  from  which  it  is  fired,  is  called  the 
gun-carriage. 

Its  principal  parts  are  : 

1.  The  axle  ; 

2.  The  wheels; 

3.  The  stock  or  flasks  ; 

4.  The  brakes  ; 

5.  The  elevating  device. 

THE  AXLE. — The  principal  parts  are  the  body,  the  rein- 
force, and  the  arms. 

The  body  is  the  middle  part  of  the  axle,  between  the 
arms,  upon  which  the  heads  of  the  cheeks  rest,  and  which 
bears  the  weight  of  the  piece  and  the  force  of  recoil.  It  is 

389 


39°  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

generally  made  of  steel,  and  is  solid,  as  this  construction  is 
necessary  to  resist  the  force  of  recoil  in  these  carriages. 
Its  length  is  governed  by  the  requirement  that  the  track  of 
the  wheels  shall  be  the  same  as  that  of  ordinary  vehicles,  so 
that  it  can  be  used  on  the  same  roads. 

Reinforce. — To  increase  the  strength  of  the  axle  and 
its  resistance  to  bending  under  the  force  of  recoil,  and  also 
to  furnish  a  support  for  the  cheeks  of  the  carriage,  the  axle 
is  generally  reinforced.  In  the  old  carriages  the  axle-body 
was  enclosed  in  wood  ;  in  the  new  field-carriages  it  is  en- 
closed between  two  steel  plates  riveted  together  and  fitting 
the  exterior  of  the  body  accurately.  For  larger  carriages, 
or  for  those  in  which  the  recoil  is  taken  up  by  hydraulic 
buffers,  this  is  not  necessary. 

The  Axle-arms. — These  form  the  supports  for  the 
wheels,  and  are  the  axes  about  which  they  revolve.  The 
arms  are  made  solid,  terminating  the  axle-body.  They 
are  conical  in  shape,  as  this  gives  stiffness  with  small 
weight,  enables  the  wheel  to  be  put  on  easily,  insures  a 
good  fit  between  wheel  and  axle-arm,  and  enables  any  wear 
to  be  taken  up  by  means  of  washers. 

The  axis  of  each  arm  is  inclined  slightly  downward  so  as 
to  make  the  lower  element  nearly  horizontal.  This  causes 
the  lower  spoke  of  the  wheel  to  stand  Vertical,  and  relieves 
it  from  cross-strain,  and  also  prevents  a  thrust  upon  the 
linchpin.  The  axis  of  the  arm  is  also  inclined  slightly  to 
the  front,  so  that  when  the  wheel  meets  any  obstacle  in  that 
direction  it  will  be  free  from  cross-strain.  These  two  in- 
clinations of  the  axle-arm  are  called  the  "  set."  The  wheel 
is  secured  on  the  arm  by  a  linchpin  which  passes  in  a 
vertical  direction  through  a  hole  in  the  end  of  the  arm,  and 
is  held  in  place  by  a  semicircular  catch  passing  under  the 
latter. 

A  shoulder  on  the  inside,  next  the  body,  holds  the  wheel 
in  place. 

220.  The  Wheels— Parts. 

The  principal  parts  are,  Fig.  203,  the  central  part  or 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         39 1 

nave  N,  the  spokes  S,  the  rim  R,  and  the  tire  T.  The  nave 
receives  the  pressure  of  the  axle  arm  and  transmits  it  to  the 
spokes.  Formerly  naves  were  made  of  wood,  and  lined 


FIG.  203. 

with  a  metal  box,  called  the  nave-box,  which  diminished  the 
wear.  Now  they  are  made  of  malleable  cast  iron  or  bronze, 
in  two  parts,  one  (a)  forming  the  nave-box  and  the  other 
(b)  forming  a  support  for  the  spokes  in  front,  which  are 
inserted  between  these  parts,  pressed  into  place  by  a  strong 
radial  pressure,  and  bolted  as  shown  at  d,  so  as  not  to 
weaken  them. 

By  this  arrangement  a  spoke  can  be  readily  removed 
and  replaced.  This  construction  is  used  in  the  Archibald 
wheel,  which  is  adopted  in  the  U.  S.  service. 

An  enlargement  c  is  sometimes  made  in  the  middle  of 
the  nave-box  to  contain  the  lubricant. 

The  spokes  s,  receive  the  pressure  from  the  nave  and 
transmit  it  to  the  rim.  In  our  service  they  are  made  of 
hickory,  as  this  gives  great  stiffness  and  elasticity  for  a 
given  weight. 

The  stiffness  is  required  to  resist  the  thrust  in  firing,  and 
strength  is  also  required  to  enable  the  wheel  to  be  used  on 
rough  ground,  where  the  spokes  are  liable  to  be  broken  by 
contact  with  obstacles.  The  spokes  are  set  at  a  slight  angle 
with  the  axis  of  the  nave,  thus  forming  a  conical  surface. 
This  is  called  the  dish,  and  its  object  is  as  follows : 

When  the  ground  is  inclined,  the  weight  of  gun  and  car- 


392  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

riage  produces  a  thrust  on  the  lower  wheel  in  the  direction 
of  the  arrow.  If  the  spokes  were  per- 
pendicular to  the  axis  of  the  nave,  this 
thrust  would  cause  a  cross-strain  on 
them,  and  its  effect  would  be  to  loosen 
them  in  the  nave,  or  cause  them  to 
FIG.  204.  work.  The  dish  enables  the  spokes  to 

resist  this  lateral  thrust,  and  it  is  converted  into  a  strain  of 
compression.  The  whole  structure  thus  acts  as  a  circular 
truss,  the  rim  being  the  tie. 

The  Rim. — This  distributes  the  weight  which  it  receives 
from  the  spokes,  to  the  ground.  It  is  generally  made  of 
wood  for  the  same  reasons  as  in  case  of  the  spokes,  and  in  sev- 
eral segments,  called  felloes.  The  object  of  this  is  to  avoid 
cutting  across  the  grain  of  the  wood,  and  consequent  weak- 
ness. 

The  Tire. — The  segments  of  the  rim  and  the  spokes  are 
held  in  place  by  the  steel  tire  T,  Fig.  203,  which  is  shrunk 
on,  and  binds  all  the  parts  together.  It  also  protects  the 
rim  from  wear,  and  when  any  of  the  parts  become  loose,  it 
can  be  removed,  shortened,  rewelded,  and  reset.  For  this 
purpose  it  is  made  of  low  steel.  It  is  held  in  place  on  the 
rim  by  countersunk  bolts  passing  through  both. 

221.  Object  of  Wheel-The  Stock. 

OBJECT  OF  WHEEL. — The  object  of  the  wheel  is  to  trans- 
fer the  resistance  to  motion  from  the  ground,  where  it  is 
great  and  irregular,  to  the  surface  of  the  axle  arm,  which 
is  lubricated,  and  the  resistance  of  which  is  consequently 
small  and  regular. 

The  power  being  applied  with  a  lever-arm,  whose  length 
is  the  radius  of  the  wheel,  while  that  of  the  resistance  or 
friction  is  the  radius  of  the  axle-arm,  the  advantage  of  the 
wheel  as  a  mechanical  power  increases  with  the  radius  of 
the  wheel,  and  decreases  with  that  of  the  axle-arm.  On  this 
account  the  radius  of  the  wheel  should  be  as  great  as  pos- 
sible and  that  of  the  axle  as  small  as  possible. 

The  radius  of  the  axle-arm  is  fixed  by  the  requirement 
oi  strength  to  support  the  shock  of  recoil;  and  that  of  the 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         393 

wheel  by  considerations  of  weight,  draught,  and  facility  of 
turning.  A  high  wheel  also  is  unstable.  These  considera- 
tions have  fixed  the  diameters  of  wheels  in  the  field  and 
siege  services  as  follows:  field  service,  5/j- inches;  siege  ser- 
vice, 60  inches.  The  siege  wheel  is  much  stronger  and 
heavier  than  that  for  the  field  service. 

An  increase  in  width  of  rim  also  distributes  the  weight 
over  a  greater  area  and  enables  the  wheel  to  better  over- 
come the  resistance  offered  by  soft  ground  to  traction ;  but 
it  increases  the  weight  of  the  wheel  and  decreases  the 
facility  of  turning. 

THE  STOCK. — This  consists  of  two  pieces,  called  the 
flasks,  which  are  separated  at  the  upper  ends,  forming  the 
cheeks,  and  which  gradually  converge  at  the  lower  ends, 
and  are  united  there  by  a  solid  piece  called  the  trail-plate 
or  lunette.  The  cheeks  rest  upon  the  axle  body  or  rein- 
forcing plates,  and  have  on  their  upper  surfaces  two  trun- 
nion-beds, in  which  the  trunnions  of  the  gun  rest.  The 
trunnions  are  held  in  place  by  two  caps,  called  cap  squares, 
which  fit  over  bolts  projecting  from  the  cheeks  at  the 
extremities  of  the  trunnion-beds,  and  are  fastened  by  keys 
or  bolts.  The  flasks  are  also  united  by  various  transoms,  to 
give  stiffness  to  the  structure.  The  supports  for  the  elevat- 
ing screw  or  other  device  are  generally  attached  to  the 
stock. 

The  distance  between  the  flasks  varies  with  the  size  of 
the  gun,  and  should  be  sufficient  to  allow  the  breech  to  be 
depressed  to  the  maximum  extent  required  in  service.  By 
this  separation,  also,  the  strain  due  to  recoil  is  distrib- 
uted over  a  greater  length  of  axle  body,  and  thus  the 
resistance  to  bending  is  increased.  The  stock  is  subjected 
to  a  strong  transverse  stress  in  firing,  and  hence  must  be 
designed  to  resist  this.  It  also  acts  to  couple  the  gun-car- 
riage to  the  limber  when  the  gun  is  to  be  transported,  and 
it  gives  the  necessary  third  point  of  support  in  firing,  and 
enables  the  piece  to  be  pointed.  To  it  are  attached  the 
supports  for  the  sponges  and  rammers,  and  in  general,  if 
possible,  no  parts  are  allowed  to  project  below  the 
plane  of  its  lower  edges,  to  avoid  striking  obstacles.  When 


394  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

not  required  to  resist  the  shock  of  firing,  its  use  is  simply 
to  connect  the  carriage  and  limber,  and  its  construction 
then  differs  materially  from  that  described,  being  much 
simpler  and  lighter. 

222.   The   Brakes — Friction-brakes — Shoe — Hotchkiss — Lemoine — 
Nordenfelt. 

BRAKES. — The  object  of  a  brake  in  the  field  and  siege 
service  is  to  limit  the  recoil,  so  that  the  piece  may  be  kept 
approximately  in  its  firing  position,  and  thus  avoid  the 
fatigue  to  the  cannoneers  of  running  the  piece  back  over  a 
considerable  distance  to  that  position  after  discharge,  and 
the  consequent  delay  in  loading. 

The  principles  of  brakes  will  be  explained  under  the 
subject  of  recoil. 

For  the  field  and  siege  services  they  may  be  divided 
into — 

1.  Friction-brakes. 

2.  Elastic  brakes. 

3.  Hydraulic  brakes. 

FRICTION-BRAKES. — These,  as  will  be  seen  later,  do  not 
give  the  best  results,  but  are  sometimes  preferred  on 
account  of  their  simplicity,  and  as  being  less  liable  to  get 
out  of  order. 

SHOE. — The  simplest  friction-brake  is  the  shoe,  which 
consists  (Fig.'2O5)  of  a  strong  piece  of  iron,  a,  fitting  the 


FIG.  205. 

wheel,  and  attached  by  a  chain,  b,  to  the  stock.  It  is 
often  used  in  travelling,  and  transforms  the  rolling  into 
sliding  friction. 


ARTILLERY   CARRIAGES— THEORY  OF  RECOIL. 


395 


THE  HOTCHKISS  BRAKE  (Fig.  206)  consists  of  a  conical 
box,  a,  working  in  screw-threads  on  the  axle-body  b.  The 
nave  of  the  wheel  is  also  made  conical  at  c. 


a 


FIG.  206. 

By  turning  the  handle  d  attached  to  the  brake,  it  is 
screwed  up  till  the  conical  surfaces  are  in  close  contact. 
The  friction  between  these  surfaces,  when  the  wheel  rotates, 
tends  to  tighten  the  brake,  and  thus  increase  the  resistance  to 
rotation,  while  if  the  moment  of  rotation  becomes  too  great, 
the  surfaces  will  slip,  and  thus  prevent  destruction  of  the 
parts. 

THE  LEMOINE  BRAKE  is  used  in  the  French  service.  It 
consists  (Fig.  207)  of  a  rope,  a,  attached  to  the  brake-beam 
at  b,  and  wound  loosely  around  the  nave  of  the  wheel. 

This  rope  is  tapering,  being  larger  at  #,  and  gradually 
decreasing  in  size.  It  is  attached  in  front  to  a  cross-bar,  c, 
and  this  is  connected  to  the  rod  d,  which  moves  freely  in 
the  direction  of  its  length,  and  carries  a  heavy  mass,  e.  The 
action  of  the  brake  is  as  follows :  When  the  piece  is  fired, 
the  carriage  recoils  in  the  direction  of  the  arrow,  while  the 
rod  d,  on  account  of  the  mass  e,  moves  relatively  forward. 
It  is  held  in  this  position  by  the  notches  on  d  bearing  against 
the  edges  of  the  plate  through  which  it  slides.  This  tight- 
ens the  cord  around  the  nave  of  the  wheel,  and  causes  it  to 
be  wound  up  as  the  wheel  turns.  Owing  to  the  increase 


396 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


in  diameter  of  the  rope,  it  is  wound  more  rapidly  as  the 
length  of  recoil  increases  and  its  velocity  decreases,  so  that 


FIG.  207. 

the  brake  is  applied  gradually.  It  may  also  be  applied 
by  hand,  in  travelling,  by  pulling  out  the  rod  d  by  the 
handle  d' '. 

NORDENFELT  BRAKE. — This  is  found  on  the  carnage  of 
the  Nordenfelt  rapid-fire  gun,  and 
also  on  the  Hotchkiss  carriage.  It 
consists  of  a  frame,  one  side  of  which 
is  shown  in  Fig.  208,  attached  to  the 
axle  above  its  centre  at  the  points 
aa ;  bb  are  the  brakes,  c  the  rod  con- 
necting them,  dd  rubber  washers 
through  which  the  brake-rods  ee  pass. 
As  the  points  of  support  a  are  eccen- 
tric with  reference  to  the  axle,  when 
the  brakes  are  lowered,  they  come 
in  contact  with  the  wheels,  and  any 
rotation  in  recoil  binds  them  still 
more  tightly.  When  not  in  use, 
they  are  hooked  up  to  the  cheeks  of 
the  carriage.  This  brake  is  elastic 
also. 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         397 

223.  Elastic  Brakes— Buffington— Englehardt — Belleville  Springs. 

ELASTIC  BRAKES. — These  check  and  moderate  recoil  by 
transmitting  the  first  shock  to  some  elastic  body,  which 
is  thereby  deformed,  and  when  this  body  resumes  its 
original  form,  clue  to  its  elasticity,  the  shock  is  gradually 
transmitted  to  the  parts  of  the  carriage.  This  relieves  the 
carriage  from  the  sudden  shock,  and  thereby  enables  it 
better  to  sustain  recoil. 

THE  BUFFINGTON  BRAKE. — This  was  designed  by  Colo- 
nel Buffington  of  the  Ordnance  Department,  and  is  used 
with  the  field  carriages. 


,C 


FIG.  209.  FIG.  210. 

The  older  form  consists  of  a  rod,  a,  Fig.  209,  surrounded 
by  a  spiral  spring  in  a  casing.  The  outer  end  of  this  rod  is 
formed  into  a  hook,  which  fits  over  the  tire  of  the  wheel. 
The  casing  which  carried  the  rod  and  spring  is  attached  to 
a  hook,  b,  above  the  centre  of  the  axle.  When  the  rod  and 
casing  are  lowered,  the  hook  rests  against  the  tire,  being 
eccentric  to  the  wheel.  Any  rotation  of  the  wheel  in  the 
direction  of  recoil  draws  the  rod  out  of  the  casing,  and  com- 
presses the  spiral  spring.  The  brake  is  thus  gradually  ap- 
plied. Various  defects  in  this  brake  have  caused  the  adop- 
tion of  the  later  form  shown  in  Fig.  210. 

Later  form  shown  in  Fig.  210.  Instead  of  the  casing 
and  spiral  spring,  the  rod  is  attached  to  a  bow-spring,  <:, 
which  is  elongated  when  the  wheel  recoils.  It  is  held  ver- 
tically when  not  in  use. 

THE  ENGLEHARDT  BUFFER.— This  is  used  on  some  of  the 
English  carriages.  It  consists  (Fig.  211)  of  an  elastic  buffer, 

a,  of  cork,  rubber,  or  springs,  which  rests  against  a  transom, 

b,  attached  to  the  cheeks  of  the  carriage. 

These  cheeks  have  a  bracket,  c,  in  front,  in  which  the 
axle  d  rests,  and  which  allows  them  to  move  backward 


398 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


independently  of  the  axle,  and  they  are  notched  in  rear  at 
e,  to  allow  a  motion  independent  of  the  cross-bar  /.  The 
axle  is  attached  to  the  cross-bar  /  by  the  brace  g,  and  this 
attachment  is  made  as  near  the  axle-arm  as  possible,  to 


a' 

y 

n--/ 

c*'    N 

h 

FIG.  211. 

avoid  bending.  A  bolt,  h,  passes  through  the  buffer  «,  and 
through  a  hole  in  the  transom  b,  and  is  attached  rigidly  to 
the  cross-bar/.  The  action  is  as  follows:  When  the  piece 
is  fired,  the  cheeks  and  transom  b  recoil  together,  the  axle 
and  cross  bar  sliding  in  their  notches  c  and  e.  This  motion 
compresses  the  buffer  #,  and  as  it  recovers  its  shape,  the 
force  of  recoil  is  gradually  transferred  to  the  wheels  and 
axle,  through  the  cross-bar /and  brace  g. 

BELLEVILLE  SPRINGS.  —  These  are   saucer-shaped  disks 
of  steel,  s,  Fig.  212,  fitted  edge  to  edge;  and  kept  in  place 


FIG.  212. 


by  an  axial  rod,  r,  for  which  purpose  a  hole  is  pierced  in  the 
centre  of  each  disk.  Since  they  occupy  a  relatively  small 
space,  a  large  number  of  them  may  be  employed,  and  the 
compression  of  each  is  small.  They  are,  however,  expen- 
sive, and  spiral  springs  are  often  used  in  place  of  them. 


ARTILLERY   CARRIAGES— THEORY  OF  RECOIL. 


399 


224.  Hydraulic  Brakes— Elevating  Devices — The  Elevating  Screw. 

HYDRAULIC  BRAKES. — These  are  not  used  in  the  field 
service,  owing-  to  their  weight,  and  liability  to  get  out  of 
order  when  subjected  to  rough  usage,  but  they  are  used  in 
the  siege  carriages,  and  in  general  wherever  the  recoil  is 
great,  and  it  is  necessary  to  regulate  it  very  exactly.  They 
will  be  considered  under  Sea-coast  Carriages,  where  they 
are  always  used. 

ELEVATING  DEVICES. — These  are  used  to  give  the  proper 
elevation  to  the  piece,  and  may  consist  of — 
A  screw  ; 
A  toothed  sector ; 
A  combination  of  levers. 

THE  ELEVATING  SCREW  is  generally  double,  and  consists 
(Fig.  213)  of  an  exterior  hollow  screw, 
#,  working  in  a  fixed  nut,  b. 

The  exterior  of  the  screw  a  has  a 
left-hand  thread,  its  interior  a  right-hand 
one.  A  second  screw,  c,  works  in  the 
interior  thread  of  a.  d  is  a  hand-wheel, 
which  is  free  to  rotate,  but  is  fixed  to 
the  nut  b,  so  that  it  has  no  motion  of 
translation.  A  longitudinal  channel  or 
spline,  e,  is  cut  on  the  exterior  of  a,  and 
a  key  on  d  fits  this.  The  action  is  as 
follows  :  When  d  is  turned  it  causes  a  to 
turn  with  it,  on  account  of  the  spline 
and  key,  and  at  the  same  time  a  working 
in  the  fixed  nut  b  moves  parallel  to  its 


—a 


FIG.  213. 


The   head   of 


being  fixed 


own   axis. 

by  a  strap,  s,  to  be  described,  cannot  turn,  and  c  is  forced 
to  move  parallel  to  its  own  axis  by  the  rotation  of  <z,  and 
the  action  of  its  interior  screw-thread.  The  resultant 
motion  is,  for  each  turn  of  d,  equal  to  the  sum  of  the  pitches 
of  the  two  screws. 

The  advantage  gained  is  that  we  are  enabled  to  use  an 
elevating  screw,  which  is  short  ordinarily,  but  which  can  be 
lengthened  to  give  any  elevation  or  depression  desired. 

Strap. — To  cause  the  blow  on  the  head  of  the  elevating 


400 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


screw,  upon  firing,  to  be  normal  to  its  axis,  and  thus  avoid 
bending,  the  nut  b,  in  which  the  screw  works,  is  arranged 
on  trunnions  between  the  cheeks  of  the  carriage,  and  a 
strap,  s,  Fig.  214,  is  attached  at  one  end  to  the  head  of  the 


FIG.  214. 

screw  c,  and  at  the  other  to  an  axis,  /,  parallel  and  near 
to  the  axis  of  the  trunnions  of  the  gun.  In  this  way  the 
axis  of  the  screw,  c,  is  kept  nearly  normal  to  the  axis  of  the 
gun  for  all  elevations. 

225.  Elevating  Devices— The  Toothed  Sector — The  Levers. 

THE  TOOTHED  SECTOR.  --  This  is  used  generally  in 
combination  with  gearing,  on  the  larger  guns.  It  consists 
(Fig.  215)  of  a  toothed  arc,  a,  bolted  to  the  gun,  and  acted 


a— -1 


FIG.  215. 


FIG.  216. 


on  by  a  gear,  b.  This  gear  may  be  worked  directly  by  a 
hand-wheel,  or  more  frequently  .by  intermediate  gearing. 
To  gain  power,  and  secure  small  motions,  a  worm-gear  is 
frequently  used. 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         401 

THE  LEVERS.  —  A  combination  of  levers,  called  a 
"4azy-tongs,"  is  used  as  an  elevating  device  on  the  light 
3.20  carriage.  It  consists  (Fig.  216)  of  the  arms  a, 
jointed  as  shown  and  attached  at  b  by  a  fixed  axis  to 
the  carriage.  Two  side  levers,  c,  are  attached  to  a  fixed 
axis  at  d  on  the  carriage,  and  to  the  arms  a  at  e.  A 
screw,  /,  passes  through  the  other  extremity  of  the  side 
levers  c,  and  works  in  two  collars,  hh,  attached  to  the  car- 
riage. When  the  screw  f  is  rotated  by  the  handle  g,  the 
side  levers  c  are  raised  or  lowered,  and  acting  on  the  arms  a 
through  its  connection  e,  it  causes  the  structure  to  elongate 
or  contract,  and  thus  to  elevate  or  depress  the  gun.  The 
device  is  connected  with  the  breech  of  the  gun  by  a  leather 
strap,  k,  passing  over  the  breech. 

226.    Draught— Modes  of  Work  of  Horse — Pack-horse— Draught- 
horse — Angle  of  Traces. 

DRAUGHT.— Field  and  siege  carriages  are  intended  not 
only  to  support  their  pieces  during  firing,  but  also  to  trans- 
sport  them  from  place  to  place.  For  this  purpose  the 
two-wheeled  gun-carriage  must  be  converted  into  a  four- 
wheeled  one,  by  the  attachment  of  a  limber.  This  leads 
to  a  consideration  of  the  load  which  can  be  carried  by  the 
horse,  and  the  best  method  of  attaching  him  to  the  carriage. 

MODES  OF  WORK  OF  HORSE.— A  horse  may  carry  his 
load  on  his  back,  in  which  case  he  acts  as  a  pack  animal ;  or 
he  may  draw  this  load  by  being  attached  to  a  carriage,  as  a 
draught  animal;  or  these  two  methods  may  be  combined. 

PACK-HORSE. — This  method  is  only  used  in  the  moun- 
tain service,  when  the  roads  are  impassable  for  wheeled 
vehicles.  Under  such  circumstances  the  load  for  a  horse  is 
from  200  to  250  Ibs.,  and,  if  moving  at  a  walk,  he  can  carry 
this  load  25  miles  in  a  day.  If  at  a  trot,  the  load  or  the  dis- 
tance, or  both,  must  be  reduced.  In  this  case  he  can  carry 
the  same  load  about  17  miles  in  a  day. 

The  daily  work  of  a  pack-horse  is  considered  equal  to 
that  of  five  men.  The  mule  is  a  better  pack  animal  than 
the  horse,  as  he  can  carry  more,  is  more  sure-footed,  and 
eats  less*.  He  is  therefore  generally  used  for  this  purpose. 


402  TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 

DRAUGHT-HORSE. — A  horse  can,  by  the  aid  of  the  wheel, 
draw  much  more  than  he  can  carry,  and  hence  it  is  always 
advantageous  to  use  him  as  a  draught  animal. 

In  considering  the  draught  of  a  horse,  his  effort  may  be 
divided  into  two  parts:  first,  that  necessary  to  start  the 
carriage,  and  second,  that  necessary  to  keep  it  in  motion.  , 

The  first  being  only  temporary,  may  approximate  the 
maximum  strength  of  the  horse,  but  it  is  important  to  know 
it,  as  upon  it  is  based  the  strength  of  the  harness. 

Experiment  shows  that  this  effort  varies  with  different 
horses  from  600  to  1000  Ibs.,  as  measured  with  a  spring 
dynamometer. 

The  second  part  of  the  effort  varies  with  circumstances, 
such  as  the  load,  nature  of  the  roads,  etc.,  from  -^  to  ^  of 
the  load.  When  horses  are  used  together  in  a  team  they 
will  do  less  work  than  the  same  number  singly,  owing  to 
their  interference  with  each  other. 

ANGLE  OF  TRACES. — The  angle  made  by  the  traces  with 
the  ground  also  influences  the  amount  of  work  done  by  a 
draught-horse. 

If  the  traces  be  attached  to  the  carriage  at  a  point  higher 
than  that  at  which  they  are  attached  to  his  shoulders,  it  is  evi- 
dent that  a  component  of  the  pull  acts  upward  and  decreases 
the  hold  of  the  horse  on  the  ground,  and,  consequently,  his 
power  to  pull.  On  the  other  hand,  if  this  point  is  below  the 
point  of  attachment  at  the  shoulder,  the  vertical  component 
acts  in  the  opposite  direction,  and  increases  his  hold  on  the 
ground.  Experiment  has  shown  that  when  the  horse  car- 
ries no  load,  the  best  result  is  obtained  when  the  traces 
make  an  angle  of  from  10°  to  12°  with  the  ground.  The 
tangent  of  12°  being  about  |-,  this  shows  that  the  horse  pulls 
best  when  \  of  his  load  is  transferred  to  his  shoulders.  On 
the  other  hand,  if  a  horse  carry  a  load  of  150  to  200  Ibs.,  and 
pull  at  the  same  time,  experiment  shows  that  this  angle 
should  be  6°  or  7°. 

Making  allowance  for  bad  roads  and  rough  usage,  ar- 
tillery horses  draw  less  than  those  of  commerce,  and  the 
loads  allowed  per  horse  are  about  as  follows : 


ARTILLERY   CARRIAGES— THEORY  OF  RECOIL.         403 

Horse  artillery,  650  Ibs. ; 
Field  artillery,  700  to  850  Ibs. ; 
Siege  artillery,  1000  Ibs. 

227.  Modes  of  Attachment  of  Horses — Attachment  of  Traces. 

MODES  OF  ATTACHMENT. — Horses  may  be  attached  to  a 
carriage  in  three  ways : 

1.  In  single  file,  with  the  wheel-horse  in  shafts; 

2.  In  double  file,  with  one  of  the  wheel-horses  in  shafts; 

3.  In  double  file,  with  the  two  wheel-horses  on  oppo- 
site sides  of  a  pole. 

The  team  is  ordinarily  composed  of  six  horses,  arranged 
in  pairs.  The  horses  nearest  the  carriage  are  called  the 
wheel-horses,  those  next  in  front  the  swing-horses,  or  swing- 
team,  and  those  in  front  the  lead-horses  or  leaders. 

In  each  team  the  left  horse  is  the  near,  and  the  right 
horse  the  off  horse.  The  near  horse  carries  the  driver. 

Single  File. — The  objections  to  this  method  of  attach- 
ment are  that  much  of  the  tractile  force  is  lost,  owing  to  the 
curving  and  turning  of  ordinary  roads ;  it  is  difficult  to 
make  all  the  horses  pull  together ;  and  the  shaft-horse,  being 
subjected  to  the  irregular  action  of  the  other  horses  of  the 
team,  is  soon  worn  out.  For  heavy  loads  over  good  straight 
roads  at  a  slow  pace,  it  has  the  advantage  of  a  direct  pull. 

Double  File,  Wheel-horse  in  SJiafts. — This  method  obviates 
the  defects  of  the  long  line  of  traction  on  ordinary  roads, 
and  it  controls  the  movements  of  the  carnage  well ;  but  it 
subjects  the  shaft-horse  to  excessive  fatigue,  and  hence  is 
not  generally  used. 

Double  File,  with  Pole. — This  method  is  generally  adopted, 
as  it  gives  the  advantages  of  a  short  line  of  traction,  with 
comparatively  little  fatigue  to  the  wheel-horses,  the  con- 
trol of  the  carriage  being  effected  by  two  horses  instead 
of  one. 

ATTACHMENT  OF  TRACES. — The  traces  may  be  attached 
to  the  carriage  by  a  single  fixed  bar,  a,  called  the  splinter- 
bar,  as  in  the  old  carriages,  or  by  a  double  tree,  b,  which  is 
pivoted  at  its  middle  point  to  the  pole,  and  the  traces 


404 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


attached  to  each  end  by  a  movable  single  tree,  c.     Fig.  217 
shows  the  old  and  the  new  methods. 


•«^y 


FIG.  217. 


The  advantage  of  the  old  method  is  that  it  is  simple  and 
strong.  The  disadvantages  are  that  it  throws  an  unequal 
amount  of  work  upon  the  two  horses,  so  that  a  willing 
horse  will  do  most  of  the  work,  and  there  is  no  method  by 
which  the  driver  can  detect  this.  Consequently,  the  re- 
sultant of  the  traction  in  this  case  will  not  coincide  with  the 
pole  or  middle  of  the  axle. 

The  advantage  of  the  new  method  is  that  it  obviates  the 
above  difficulty,  and  forces  an  unwilling  horse  to  do  his 
share  of  the  work.  The  single  trees  also  prevent  chafing, 
by  yielding  to  the  motion  of  the  horse  as  he  advances  his 
shoulders  in  pulling. 

228.  Support  of  Pole— Line  of  Draught  of  Traces. 

SUPPORT  OF  POLE.  —  The  weight  of  the  pole  may  be 
supported— 

1.  By  counterbalancing  it  in  rear  of  the  axle ; 

2.  By  suspending  it  from  the  necks  of  the  horses ; 

3.  By  a  combination  of  these  methods. 
Counterbalancing  Weight  of  Pole. — The  advantage  of  this 

method  is,  that  it  frees  the  necks  of  the  horses  from  the 
weight  of  the  pole,  and  they  are  consequently  not  fatigued 
by  it. 

The  disadvantages  are,  that  if  it  is  done  by  placing  the 
trunnions  of  the  gun  well  to  the  rear  on  the  gun-carriage,  it 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL. 


405 


causes  difficulty  in  limbering,  because  of  the  extra  weight 
lifted.  If  it  is  done  by  allowing  the  trail  to  project  over 
the  pintle  hook  and  rest  upon  a  circular  sweep-bar,  a,  Fig. 
218,  it  is  difficult  to  limber,  as  the  trail  must  be  raised  suffi- 


l 


FIG.  218. 

ciently  to  pass  over  the  pintle  b.  As  quickness  of  limbering 
is  of  importance  with  field  artillery,  this  method  is  not  used. 

In  the  siege  service,  where  quickness  is  not  required, 
-and  where  the  weights  are  relatively  great,  it  is  used,  espec- 
ially th'e  method  shown  in  Fig.  218. 

Suspending  Weight  from  Necks  of  Horses. — The  advantage 
of  this  method  is  that  the  attachment  of  the  trail  to 
the  limber  can  be  made  at  the  most  convenient  place  for 
limbering,  and  the  weight  of  the  gun  can  be  thrown  so 
far  forward  as  to  render  the  operation  of  limbering  very 
easy.  The  great  objection,  however,  is  that  it  fatigues  the 
horses  too  greatly,  and  cannot  be  used. 

Hence  a  combination  of  these  two  methods  has  been 
adopted  in  the  field  service.  To  diminish  the  weight  rest- 
ing on  the  necks  of  the  horses,  the  ammunition-chest  of  the 
limber  has  been  placed,  so  that  its  centre  of  gravity  when 
loaded  is  directly  over  the  axis  of  the  axle,  and  the  weight 
upon  the  trail  when  the  gun  is  limbered  is  regulated  to 
partly  counterbalance  that  of  the  pole. 

LINE  OF  DRAUGHT  OF  TRACES.  —  This  is  so  arranged 
that  the  line  of  traction  shall  be  continuous  from  the  lead- 


406  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

horses  to  the  carriage,  and  is  accomplished  by  attaching  the- 
traces  of  the  swing-team  directly  to  those  of  the  wheelers,, 
and  those  of  the  lead-team  directly  to  the  traces  of  the 
swing-team.  By  this  means  each  horse  pulls  independently 
of  all  the  others,  and  there  is  no  interference. 

229.  Turning  Angle — Direction  of  Carriage — Backing. 

TURNING  ANGLE. — The  angle  required  to  turn  the  car- 
riage in,  is  called  the  turning  angle,  and  is  measured  by  one 
half  the  horizontal  angle  through  which  the  pole  sweeps. 
In  practice  an  angle  of  60°  is  sufficient.  It  varies  with  the 
arrangement  of  the  horses,  the  height  of  the  front  wheels, 
the  length  of  stock,  the  position  of  the  pintle,  and  the  thick- 
ness of  the  stock  at  the  point  where  the  front  wheels  strike 
it.  Other  considerations  determine  that  the  height  of  the 
front  wheels  shall  be  the  same  as  those  of  the  rear  ones  for 
interchangeability,  that  the  length  of  stock  shall  be  gov- 
erned by  considerations  relating  to  recoil,  and  that  the 
position  of  the  pintle  shall  be  considered  with  reference  to 
ease  of  limbering  and  weight  of  pole  on  the  horses'  necks, 
as  before  explained.  For  carriages  that  do  not  withstand 
the  shock  of  recoil,  the  length  of  stock  is  adjusted  with 
reference  to  the  turning  angle. 

DIRECTION  OF  CARRIAGE. — This  is  given  by  means  of 
the  pole.  The  latter  being  attached  to  the  necks  of  the 
wheel-horses,  the  direction  may  readily  be  changed  by 
directing  the  wheel-team  to  the  right  or  left. 

BACKING. — The  pole  is  also  used  to  stop  and  back  the 
carriage.  The  wheel-horses  are  attached  to  the  front  of  the 
pole,  as  will  be  explained  when  the  harness  is  described. 

In  stopping  or  backing  the  backward  thrust  of  the  horses 
is  applied  at  the  end  of  the  pole,  and  this  thrust  transmitted 
to  the  rear  along  the  pole  to  the  carriage. 

230.  The  Harness. 

The  harness  at  present  in  use  for  the  field  artillery  was 
designed  by  Major  Williston  of  the  artillery.  That  for  the 
wheel-team  differs  slightly  from  the  swing  and  lead  harness.. 
For  the  wheel-team  it  consists  of — 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.'       407 

1.  The  head  gear  to  guide  and  hold  the  horses; 

2.  The  saddle  to  transport  the  driver; 

3.  The  draught  harness,  by  which  the  carriage  is  moved 
forward ; 

4.  The  breeching,  by  which  the  carriage  is  stopped,  or 
moved  to  the  rear ; 

5.  The  breast  straps,  by  which  direction  is  given  to  the 
carriage,  and  the  weight  of  the  pole  supported. 

For  the  swing  and  lead  teams  the  breeching  and  breast 
straps  are  omitted,  and  the  traces  are  supported  by  a  single 
hip  strap. 


FIG.  219. 

Head  Gear. — The  head  gear  consists  (Fig.  219)  of  the 
bridle  a,  by  which  the  horse  is  guided,  and  the  halter  for 
holding  him  when  not  in  the  carriage. 

The  bridle  and  halter  are  the  same  as  those  used  in  the 
cavalry  service.  The  bridle  rein  of  the  off  horse  passes 
through  a  pulley  on  the  front  of  his  saddle,  so  that  there  is 
a  direct  instead  of  an  oblique  pull,  in  stopping  and  backing. 

Saddle. — The  saddle  x  is  the  same  as  that  used  in  the 
cavalry  service.  Each  horse  is  saddled,  the  saddle  being- 
held  in  place  and  motion  to  the  front  prevented  by  the 
back  strap  t  and  crupper  t' ,  while  the  collar  is  secured  to 


408  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

the  saddle  in  front  by  the  strap  v.  The  girth  strap  or 
cincha  w  prevents  motion  of  the  saddle  around  the  horse. 
The  near  horse  carries  the  driver,  and  the  off  horse  may 
carry  an  extra  cannoneer.  Saddle-bags,  b,  are  used,  as  in 
the  cavalry  service,  to  carry  the  clothing,  etc.,  of  the  drivers. 

Draught  Harness. — This  consists  of  a  collar,  c,  made 
of  U-shaped  steel.  It  is  hinged  at  the  top,  and  closes  at  the 
bottom  with  a  spring  catch.  It  rests  against  the  shoulders 
of  the  horse,  and  is  intended  to  distribute  the  force  of  trac- 
tion over  a  greater  area,  and  thus  prevent  chafing. 

A  strong  leather  tug,  d,  is  attached  to  each  branch  of 
the  collar,  and  at  the  outer  end  of  the  tug  is  an  iron  ring,  e, 
through  which  the  front  trace-chain  f  passes. 

The  trace  g  is  a  stout  leather  strap,  terminated  at  the 
front  end  by  a  chain  and  toggle,  /  and  at  the  rear  end  by  a 
ring,  through  which  passes  the  rear  trace-chain  //,  having  at 
one  end  a  hook  and  at  the  other  end  the  spring  /.  The  rear 
ends  of  the  trace-chains  y,  of  the  swing  horses,  are  attached 
directly  to  the  front  trace-chains  /of  the  wheel-horses,  thus 
giving  a  continuous  line  of  traction  throughout  the  teams. 
The  loin  strap  u  supports  the  traces  at  their  middle  point. 
The  trace-chains  of  the  wheel-horses  are  attached  to  the 
single  trees  z,  and  in  unharnessing,  these  are  detached  from 
the  double  tree,  and  hooked  to  the  rear  of  the  saddle,  for 
which  purpose  a  hook,  k,  is  provided.  The  spring  /  is  used 
to  attach  the  traces  of  the  wheel-horses  to  the  single  trees  i. 
This  allows  a  gradual  starting  of  the  carriage,  and  thus 
diminishes  the  fatigue  of  the  horses,  and  the  strain  on  the 
harness. 

Breeching. — This  consists  of  a  breech  strap  m,  hip  straps 
ss',  two  side  straps  s",  and  a  broad  flat  strap  or  martingale,  n. 
The  breech  strap  m  passes  around  the  hind-quarters  of  the 
horse,  and  is  supported  by  the  hip  straps  ss',  two  on  each  side. 
The  breech  strap  is  joined  to  the  martingale  n  by  the  two 
side  straps  s".  The  martingale  n  passes  along  under  the 
horse,  and  between  his  forelegs  to  the  front,  where  it  is  con- 
nected to  a  transverse  bar,  o,  on  the  front  end  of  the  pole, 
called  the  neck  yoke.  This  yoke,  o,  is  of  wood,  and  has  a 
ring,  p,  attached  at  its  middle  point,  which  slips  over  the 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         409 

-end  of  the  pole,  and  rests  against  a  stop,  q,  on  the  under 
side.  The  collars  of  the  wheel-horses  are  attached  to  the 
ends  of  the  neck  yoke  o  by  the  breast  straps  r. 

In  backing,  the  pressure  is  exerted  by  the  horse  against 
the  breech  strap  m,  and  this  pressure  is  transmitted  through 
the  side  straps  s"  and  the  martingale  n,  to  the  neck  yoke  <?, 
and  thence  to  the  pole. 

The  action  of  the  harness  may  be  understood  from 
Figs.  220  and  221.  For  draught  and  direction  t  represents 

,-t  ,-t    b         ,-t 


.SU 


'    *> — ff*fh* 

r-d 


L 


FIG.  220. 


the  traces,  s  the  single  trees,  d  the  double  tree,  b  the  breast 
straps,  c  the  collar.     For  breeching  b'  is  the  breech  strap, 

'm    .XT^N       »    J  ^6  s^e  straPs>  ;;*  tne  martingale, 
-''"      n  the  neck  yoke. 

The  great  advantage  of  the  pres- 
ent   harness    over    the    old    is    the 
change  in  the  breeching,  by  which 
FIG.  221.  the  horse  has  a  direct  instead  of  an 

oblique  thrust  to  the  rear.     Many  other  improvements  are 
embodied  in  it. 

CARRIAGES  FOR  flOUNTAIN  AND  FIELD  ARTILLERY. 

231.  Carriage  for  Hotchkiss  Mountain  Gun — For  3.6  Field  Mortar. 

HOTCHKISS  MOUNTAIN  CARRIAGE  (Fig.  222).— -The  flasks 
a  are  made  of  steel  strengthened  with  angle-irons,  b,  and  with 
three  transoms,  c,  d,  e,  and  a  trail-plate,  g.  The  axle  is  solid, 
and  the  wheels  have  bronze  naves.  Recoil  is  checked  when 
necessary,  by  a  rope  tied  around  the  spokes  of  the  wheels, 
and  passing  over  the  stock. 

The  elevating  screw  passes  through  the  transom  e.     For 


4io 


TEXT- BOOK  OF  ORDNANCE   AND    GUNNERY. 


draught,  a  pair  of  shafts  is  attached  to  the  trail  by  the  hook 
h  and  a  pin,  and  the  gun  and  carriage  drawn  by  one  mule. 
The  gun  and  carriage  are  generally  packed  on  two  mules, 


Jh 


FIG.  222. 

and  the  ammunition  carried  in  boxes  on  mules  also.  Weight 
of  carriage,  220  Ibs.  The  carriage  for  the  3-inch  gun  is 
similar  to  this. 


FIG.  223. 

3.6  MORTAR  CARRIAGE  (Fig.  223).  —  This  carriage  is 
made  of  cast  steel,  in  a  single  piece,  provided  with  a  clamp- 
ing device  in  front,  which  bears  against  a  steel  arc  attached 
to  the  mortar. 

Elevation  is  given  by  the  quadrant,  and  the  mortar 
clamped  in  position  by  the  clamping  device.  When  in  use 
the  carriage  rests  on  a  wooden  platform,  and  recoil  is 
checked  by  a  heavy  rope  attached  to  stakes  in  front. 


AR  TILLER  Y    CARRIA  GES—  THEOR  Y   OF  RECOIL.         4  * l 

232.  3.2-inch  Field-gun  Carriage. 

This  carriage  was  designed  by  Colonel  Buffington  of  the 
Ordnance  Department.     Its  principal  features  are — 

1.  The  method  of  reinforcing  the  axle; 

2.  The  formation  of  the  flasks  ; 

3.  The  elevating  device  ; 

4.  The  brake. 

Reinforcing  Axle.  --  To  stiffen   the   axle   against   recoil, 
the  body  is  enclosed  (Fig.  224)  between  two  plates  of  steel, 


FIG.  224. 

which  are  riveted  together  temporarily,  bored  out  to  a 
diameter  slightly  less  than  that  of  the  exterior  of  the  axle 
body,  and  the  plates  then  riveted  tightly  together.  The 
width  of  these  plates  is  in  the  plane  of  the  lower  edges  of 
the  flasks,  and  hence  they  resist  the  force  of  recoil.  They  also 
serve  as  supports  for  the  flasks  which  are  bolted  to  them. 

Formation  of  Flasks. — Each  flask  (Fig.  225)  is  formed 
of  two  pieces  of  sheet  steel,  stamped  while  hot  between 
dies  into  the  shape  shown,  and  riveted 
together  through  the  flanges.  The 
lower  edge  a  of  the  outer  piece  of 
each  flask  projects  inward,  forming 

N^a       a/  a''       a  flange,  to  which  the  transoms  are 

FIG.  225.  riveted,  and   by  which  the  flasks  are 

bolted  to  the  axle  plates.  The  flasks  are  connected  by 
transoms,  three  of  which  form  a  tool-box,  with  a  hinged  lid, 
for  carrying  tools,  oil-can,  and  loose  primers. 

The  above  construction  gives  great  lateral  and  vertical 
stiffness.  The  lower  ends  of  the  flasks  converge  to  a  trail- 
plate,  at  the  extremity  of  which  is  the  lunette  ring,  by  which 
the  carriage  is  hooked  to  the  limber. 

Elevating  Device. — This  is  an  assemblage  of  jointed 
levers,  previously  described,  called  a  "  lazy  tongs." 


412 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


Brake. — The  bowspring  brake  is  used. 

Minor  Parts. — The  wheels  are  of  the  Archibald  pat- 
tern. The  trail  handspike  is  made  of  two  pieces  of  wood 
split  axially,  arid  having  a  sheet  of  steel  between  them,  the 
whole  bound  together  by  a  series  of  rings.  The  handspike 
is  hinged  to  the  trail-plate,  and  when  not  in  use  is  folded 
against  the  trail,  and  held  in  place  by  a  spring  catch. 

There  are  two  seats  for  cannoneers  on  the  axle.  The 
flasks  also  carry  the  supports  for  the  sponge  and  rammer, 
etc. 

The  complete  gun-carriage  is  shown  in  Fig.  226. 


FIG.  226. 
233.  The  Limber. 

The  principal  parts  of  the  limber  are — 

1.  The  wheels  and  axle  ; 

2.  The  pole ; 

3.  The  supports  for  the  ammunition-chest ; 

4.  The  ammunition-chest. 

Wheels  and  Axle. — The  wheels  are  the  same  as  those 
of  the  gun-carriage.  The  axle  is  of  steel,  but  as  it  does  not 
withstand  the  shock  of  recoil,  it  is  not  reinforced. 

The  Pole. — This  consists  of  two  parts,  one  of  which  is 
permanently  attached  to  the  limber,  and  is  called  the  fork, 
a  (Fig.  227),  and  the  other  the  pole  proper,  b. 

The  fork  is  of  steel,  of  this  section,  [""  "1 ,  and  is  attached 
to  the  axle-body.  It  is  prolonged  to  the  rear,  and  carries 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         413 

upon  its  rear  end  the  pintle-hook  c  and  key  d.  The  pole  b 
is  made  of  light  elastic  wood,  and  as  it  may  be  broken,  is 
held  in  the  fork  by  a  bolt,  e,  and  can  be  readily  removed 
and  replaced.  Its  outer  end  carries  a  pad,  f,  to  prevent 
injury  to  the  swing-horses,  and  a  stop,  g,  against  which  the 
neck  yoke  rests ;  h  is  the  double  tree  held  by  a  bolt,  t. 


FIG.  227. 

Supports  for  Ammunition-chests. — The  ammunition-chest 
/  (Fig.  229)  is  supported  by  the  fork,  and  by  the  two 
hounds  £.  These  hounds  are  braced  to  the  fork  in  rear,  and 
are  connected  together  in  front,  and  also  to  the  fork,  by  a 
cross-bar/. 

The  hounds  not  only  support  the  chest,  but  they 
strengthen  all  the  parts,  and  assist  in  transmitting  the  force 
of  traction  to  the  axle.  The  chest  is  bolted  to  the  hounds 
front  and  rear.  The  hounds  and  fork  also  support  the  foot- 
boards m  (Fig.  229),  upon  which  the  feet  of  the  cannoneers 
rest. 

Ammunition-chest. — This  is  made  of  wood  for  lightness. 
It  carries  the  ammunition  for  the  immediate  supply  of 
the  gun,  and  is  of  the  same  size  as  the  chests  of  the  caisson 
for  interchangeability.  It  also  furnishes  seats  for  the  can- 
noneers. 


414 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


The  lid  opens  on  top.  The  advantage  of  this  is  that  the 
chest  can  be  made  waterproof  until  the  water  reaches  the 
lid.  Its  disadvantage  is  that  the  ammunition  is  less  accessi- 
ble than  if  the  lid  opened  on  the  rear  side.  The  advantage 
in  case  of  field  artillery  outweighs  the  disadvantage,  since 
the  cartridges  for  this  service  are  carried  in  bags,  and  hence 
the  ammunition  would  be  spoiled  by  access  of  water.  For 
metallic  ammunition,  as  with  machine  guns  and  the  revolv- 
ing cannon,  as  they  are  not  liable  to  damage  by  water,  the 
lid  opens  on  the  side  for  accessibility. 

The  interior  of  the  chest  is  divided  into  three  parts  by 
two  partitions  (Fig.  228).  The  projectiles  are  placed  up- 
right in  the  end  divisions  a,  and  th'e 
cartridges  in  the  middle  division  b. 
The  cartridges  are  thus  in  a  measure 
protected  from  fire  by  the  pro- 
jectile. The  chest  is  low,  so  that  a 
man  of  ordinary  height  can  easily 


a 


a 


To  avoid  accident,  no 


FIG.  228. 
get  at  the  ammunition. 

Each  chest  carries  42  rounds, 
primers  are  carried  in  the  chest. 

Packages  of  primers  are  carried  in  the  cylindrical  boxes, 
with  screw  tops  (n,  Figs.  227  and  229),  and  loose  primers  in 
the  tool-box  of  the  gun-carriage. 


FIG.  229. 

The  limber  complete  is  shown  in  Fig.  229.     The  descrip- 
tions of  the  caisson,  forge  and  battery  wagon,  and  artillery 


ARTILLERY   CARRIAGES— THEORY  OF  RECOIL. 


415 


store- wagon,  are  omitted.     The  carriage  and  limber  for  the 
3.6-inch  field-gun  resemble  those  for  the  3.2-inch  gun. 


CARRIAGES  FOR  SIEGE  ARTILLERY. 

234.  5-inch  Siege-gun  Carriage. 


FIG.  230. 

This  carriage  (Fig.  230)  is  made  of  steel  plate  -J  inch 
thick,  the  cross-section  of  the  flasks  being  as  shown  at  A. 

The  cheeks  are  united  by  two  transoms,  b,  c,  in  front,  and 
connected  in  rear  of  c,  as  shown  in  figure  A.  The  axle  r  is 
of  steel  and  hollow.  The  elevating  device  is  a  double 
screw  e,  connected  by  a  strap  d  with  an  axis  d' ,  parallel  to 
and  under  the  trunnions.  The  object  of  the  strap  has  been 
explained. 

Recoil  is  checked  by  a  hydraulic  buffer,  s,  which,  when 
the  gun  is  in  the  firing  position,  is  connected  by  straps /to 
a  bolt,  g,  on  the  platform.  The  piston-rod  of  this  buffer  is 
attached  to  the  carriage  by  a  lug,  h.  Figure  B  shows  the 
arrangement  of  buffer  and  straps  for  attachment  to  bolt  on 
platform ;  k  is  the  travelling  trunnion-bed,  only  one  being 
shown ;  /  is  the  lunette  plate  and  lunette.  When  arranged 
for  travelling,  the  pintle  of  the  limber  passes  through  /,  the 
gun  is  moved  back  into  the  travelling  trunnion-beds  k,  the 
hydraulic  buffer  occupies  the  position  «/,  and  the  elevating 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

screw  the  position  n.  The  principal  characteristic  of  the 
carriage  is  the  height  of  the  trunnion-beds,  which  are  72.25 
inches,  or  6  ft.  i  in.  from  the  ground.  This  is  to  enable  the 
gun  to  be  fired  over  a  parapet  of  sufficient  height  to  shelter 
the  gunners. 

235.  7-inch  Siege-howitzer  Carriage. 

This  carriage  (Fig.  231)  is  made  of  steel  plate  f  inch 
thick,  the  cross-section  of  the  flasks  being  similar  to  that  of 
the  siege  carnage.  The  cheeks  are  held  together  by  tran- 
soms, and  the  axle  is  solid.  The  carriage  differs  from  the. 
5-inch  in  the  following  points: 


FIG.  231. 

The  cheeks  are  cut  out  at  ab  to  decrease  the  weight. 
The  piece  is  supported  on  sliding  trunnion-pieces,  e.  In 
front  are  two  hydraulic  buffers,  d,  which  limit  the  recoil  of 
the  trunnion-pieces  c  to  about  six  inches.  In  rear  of  the 
sliding  trunnion-pieces  c  are  two  sets  of  Belleville  or  spiral 
springs  ^,  which  return  the  piece  to  its  firing  position  upon 
the  carriage.  The  rod  upon  which  the  springs  are  strung 
passes  through  a  hole,  /,  in  the  travelling  trunnion  beds  n. 

The  recoil  of  the  carriage  is  checked  by  the  buffer  g, 
attached  as  in  the  5-inch  siege-carriage.  The  elevating 
device  consists  of  a  rack,  h,  bolted  to  the  howitzer,  in  which 
works  a  worm,  t,  mounted  between  two  lugs,/,  on  the  slid- 
ing trunnion-piece  c. 


ARTILLERY    CARRIAGES— THEORY   OF  RECOIL.         417 

A  splined  or  square  shaft,  k,  passes  through  this  worm 
and  its  lugs,/,  and  fits  loosely,  so  that  the  worm  may  slide 
along  the  shaft.  When  recoil  occurs,  the  trunnion-car- 
riages slide  to  the  rear  along  the  upper  surface,  m,  of  the 
cheeks,  carrying  with  them  the  piece  and  the  elevating- 
gears  //  and  i.  The  springs  e  then  act  to  force  the  gun 
and  elevating  gear  back  into  position.  With  this  carriage 
the  first  shock  of  recoil  is  taken  up  by  the  upper  buffers,  d, 
and  the  strain  gradually  transmitted  to  g.  The  carriage 
can  thus  be  made  lighter  and  stronger. 

236.  7-inch  Siege-mortar  Carriage. 


FIG.  232. 


This  carriage  (Fig.  232)  is  made  of  steel  plate  as  in  the 
case  of  the  5  and  7-inch  wheeled  carriages,  and  in  its  method 
of  checking  recoil  and  restoring  the  piece  to  the  firing  posi- 
tion it  resembles  the  7-inch  howitzer  carriage.  It  differs, 
however,  in  many  particulars. 

It  is  not  a  wheeled  carriage,  but  is  intended  to  rest  upon 
a  platform  when  the  piece  is  fired,  like  the  old  smooth-bore 
mortar  carriages.  Two  hydraulic  buffers,  a,  in  front,  check 
the  recoil,  while  the  coiled  springs  b  in  rear  of  the  sliding 
trunnion-pieces  c,  return  the  piece  to  the  firing  position. 
These  coiled  springs  are  enclosed  in  a  telescopic  or  sliding 
case,  de,  the  part  d  sliding  over  e  in  recoil. 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  platform  has  three  traverse-circles,/,  bolted  to  it, 
and  also  two  clamping-circles  g.  Flanges,  //,  on  the  mortar 
carriage  fit  under  these  clamping-circles,  and  retain  the  car- 
riage in  place,  preventing  its  recoil.  Lugs,  i,  are  attached  to 
the  carriage,  against  which  handspikes,  /,  rest.  The  lower 
ends  of  these  handspikes  are  shod,  and  fit  into  teeth,  k,  on 
the  clamping-circles.  By  moving  the  handspikes,  the  mor- 
tar carriage  may  be  traversed  in  azimuth  for  pointing. 
Elevation  is  given  by  a  bar,  /,  which  is  inserted  in  radial 
grooves  formed  in  a  piece  of  wrought  iron,  m,  bolted  to  the 
trunnion.  The  cheeks  are  connected  by  transoms  to 
strengthen  them,  and  are  cut  out  at  o  for  lightness. 


CARRIAGES  FOR  SEACOAST  ARTILLERY. 

237.  Classification  —  Barbette  Carriages  —  Barbette  Carriage  for 
8-inch  Rifle  —  Principal  Parts  —  Base-plate  —  Rollers  and 
Distance-rings. 

CLASSIFICATION. — Seacoast  carriages  are  classed  into — 

1.  Barbette; 

2.  Casemate  or  turret ; 

3.  Disappearing; 

according  as  the  piece  is  fired  over  the  parapet;  through 
a  port  or  embrasure  ;  or  over  the  parapet,  the  gun  recoiling 
below  it  on  discharge. 

BARBETTE  CARRIAGES. — The  barbette  carriages  for  8,  10 
and  12-inch  guns  resemble  each  other  in  general,  differing 
only  in  certain  details  of  construction  on  account  of  the 
varying  weight  of  the  guns.  The  8  and  lo-inch  carriages 
are  made  principally  of  cast  iron,  the  12-inch  of  cast  steel. 
The  8-inch  carriage  may  be  taken  as  a  type  of  the  others, 
and  will  be  described. 

CARRIAGE  FOR  S-INCH  RIFLE — PRINCIPAL  PARTS. — The 
principal  parts  of  the  carriage  (Figs.  233  and  234)  are: 

1.  The  base-plate  or  lower  roller  path,  A  ; 

2.  The  rollers  and  distance-rings,  B ; 

3.  The  chassis,  C; 

4.  The  top  carriage,  D. 


ARTILLERY  CARRIAGES— THEORY  OF  RECOIL.         419 


FIG.  233. 


DlC" IfTlfl      PfT~lir  III!      Ill — 11 


FIG.  234. 


420 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


BASE-PLATE. — This  consists  of  a  heavy  casting,  A,  shown 
in  plan,  section,  and  elevation,  Fig.  235.  It  rests  upon  a 
bed  of  concrete,  to  which  it  is  bolted  by  the  anchor-bolts  a  \ 
b  is  the  roller-path  upon  which  rests  a  series  of  conical 
forged  steel  rollers,  E.  The  central  portion,  c,  corresponds 
to  the  pintle  in  the  old  carriages,  and  around  it  fits  a  collar, 
d,  Fig.  236,  upon  the  chassis,  so  that  rotation  in  azimuth 
occurs  about  this  central  projection. 

ROLLERS  AND  DISTANCE-RINGS.  —  A  ring  of  conical 
forged  steel  rollers,  E,  Fig.  235,  rests  upon  the  roller-path 


FIG.  235. 


b  of  the  base-plate,  and  upon  these  rests  the  corresponding 
upper  roller-path,  c,  Fig.  236,  of  the  chassis.  These  rollers 
are  shaped  as  shown  at  E,  the  object  of  the  flange  d  being 
to  keep  the  rollers  in  place  by  its  bearing  on  the  inner 
edge  of  the  roller-path.  For  the  8-inch  carriage  there 
are  twenty  of  these  rollers.  They  are  held  in  place  by 
two  distance-rings,  B,  which  are  slotted  for  the  axis  of  the 
rollers  as  shown  at  e.  The  distance-rings  are  kept  in  place 
and  braced  by  the  braces/ 

338.  8-inch  Barbette  Carriage— The  Chassis. 

This  consists  (Figs.  234  and  236)  of  the  circular  horizon- 
tal part  a  and  the  two  vertical  cheeks  b.     The  circular  part, 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL. 


421 


a,  supports  the  cheeks,  and  carries  on  its  lower  side  the 
upper  roller  path  c,  and  the  central  collar  d,  which  fits  over 
the  corresponding  central  projection,  Fig.  235,  in  the  base- 
plate. The  upper  surfaces  e  of  the  cheeks  b  are  inclined  to 
the  front,  and  carry  at  their  forward  ends  the  lugs /which 
hold  the  piston-rods  of  the  hydraulic  buffers. 

In  modern  carnages,  the  irregularities  due  to  sliding 
friction  are  avoided  by  placing  the  top  carriage  on  rollers, 
and  throwing  all  the  work  of  checking  the  recoil  upon  the 
buffers,  which  can  be  very  accurately  regulated. 

These  rollers  are  shown  at  £•  inserted  in  recesses  in  the 


FIG.  236. 

chassis-rail,  and  rotating  on  journals,  so  that  the  exterior  of 
the  roller  is  just  above  the  chassis-rail. 

The  device  for  traversing  in  azimuth  is  shown  in  front 
and  in  plan  in  Fig.  234.  It  consists  of  a  cross-shaft,  /z,  with 
cranks.  This  shaft  carries  a  worm,  z,  gearing  into  a  worm- 
wheel,  /,  which  works  upon  an  axis,  k,  attached  to  the 
chassis. 

In  rear  of  the  worm-wheel  is  a  sprocket-wheel,  /,  on  the 
same  shaft  withy  and  attached  to  it,  so  that  one  cannot  turn 
independently  of  the  other.  A  chain,  m,  is  attached  at  one 
end  to  the  bed-plate  at  n,  and  the  other  end  of  the  chain  at  a 
corresponding  point  near  the  first,  not  shown  in  drawing. 

This  chain  passes  under  a  small  wheel  in  a  fork  at  o  and 


422 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


thence  over  the  sprocket-wheel  /.  When  motion  is  given 
to  /  by  the  shaft,  worm,  and  cranks,  the  chain  will  pass  over 
the  sprocket-wheel  and  the  chassis  turn  on  its  rollers,  E. 
Vertical  motion  of  the  chassis  is  prevented  by  clips,  #,  bolted 
to  it  and  embracing  a  flange,  y,  on  the  bed-plate. 

The  device  for  hoisting  the  ammunition  is  shown  in  rear 
of  the  chassis.  The  projectile  is  run  up  on  a  truck  (see  Fig. 
233),  and  is  then  lifted  together  with  the  loading-tray  by  the 
lever/.  This  lever  is  on  a  horizontal  shaft,  q,  which  carries 
a  worm-gear,^-,  acted  on  by  the  worm  s  on  the  shaft  t.  Its 
action  is  evident. 

239.  8-inch  Barbette  Carriage— The  Top  Carriage  and  Buffers — 
Elevating  Device. 


,e 


FIG.  237. 

THE  TOP  CARRIAGE  AND  BUFFERS. — These  are  shown 
in  Fig.  237  in  section  and  elevation.  The  top  carriage 
carries  the  gun,  and  consists  of  a  single  casting,  comprising 
the  buffers  b,  and  their  connecting  transom,  a.  On  the  top 
of  .each  buffer  is  cast  the  bracket  c,  carrying  the  trunnions  of 
the  gun. 

This  top  carriage  rests  on  the  rollers  of  the  chassis-rail, 
as  shown  in  section,  and  is  held  in  place,  and  prevented  from 
lifting  at  discharge,  by  the  flanges  d.  In  the  section  are  also 
shown  the  ribs  or  throttling-bars,  e,  which  regulate  the  flow 
of  liquid  in  the  buffers,  there  being  two  in  each  cylinder, 
held  in  place  by  bolts  passing  through  the  walls  of  the 
cylinders.  The  action  of  these  buffers  will  be  explained 
under  the  subject  of  Recoil. 

A  cross  pipe,  /,  called  ah  equalizing  pipe,  connects  the 
liquid  in  the  two  cylinders,  and  insures  their  uniform  resist- 
ance. 


ARTILLERY  CARRIAGES— THEORY   OF  RECOIL. 


423 


The  pistons  and  rods  are  removed,  by  unscrewing  the 
nuts,  g,  which  close  the  rear  ends  of  the  cylinders,  and  then 
by  removing  the  locking  and  piston  nuts  h,  t,  the  piston  and 
rod  can  be  pushed  out  to  the  rear. 

The  recoil  is  limited  to  40  inches. 

ELEVATING  DEVICE. — This  is  shown  in  Fig.  238.  It 
consists  of  a  square  shaft,  a,  attached  to  the  right  side  of  the 
chassis,  and  working  in  fixed  bearings  at  b  and  c\  d\s  a 
sliding  bearing  attached  to  the  top  carriage.  In  this  bear- 
ing works  a  bevel-gear,  e,  gearing  into  a  second  bevel-wheel, 
f,  on  the  vertical  shaft,  g,  attached  to  the  top  carriage.  A 
worm,  h,  on  this  shaft  gears  into  the  worm-wheel  i,  on  the 
horizontal  shaft/,  and  on  this  same  shaft/ is  a  second  gear- 


m 


FIG.  238. 


wheel,  k,  engaging  with  the  rack  /,  on  the  gun.  When  recoil 
occurs,  the  sliding  bearing  d,  moves  along  the  square  shaft  a, 
carrying  with  it  the  bevel-gear  e,  so  that  the  gears  are  con- 
stantly engaged,  and  the  gun  can  be  elevated  in  any  posi- 
tion. The  return  to  battery  carries  the  gear  e  along  the 
shaft  a.  By  means  of  the  hand-wheels  m  and  «,  the  gun  may 
be  elevated  from  front  or  rear.  The  return  of  the  piece  to 
the  firing  position  is  due  to  gravity.  Carriages  of  this  kind 
are  called  gravity  return  carriages. 

240.  The  12-inch  Mortar  Carriage — General  Features — Springs. 
GENERAL  FEATURES. — This  carriage  consists  of — 

1.  The  bed-plate  or  lower  roller-path  A  ; 

2.  The  rollers  and  distance-rings^; 

3.  The  upper  roller  path  or  racer  C\ 


424 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


4.  The  cheeks  D\ 

5.  The  spiral  springs^,  and  the  hydraulic  cylinders  H. 
The  upper  roller-path  is  circular,  and  supports  the  cheeks, 

which  are  vertical,  the  two  together  forming  the  top  car- 
riage. The  lower  roller-path  is  also  circular. 

SPRINGS. — On  the  side  of  each  cheek  is  cast  a  cylindrical 
recess,  E  (Figs.  239  and  240),  which  contains  a  column  of 
spiral  springs,  F. 

These  springs  are  in  ten  separate  lengths,  and  each 
length  is  composed  of  two  coils,  an  inner  one,  F' ,  and  an 


FIG.  239. 

outer  one,  F.  A  pile  of  Belleville  springs,  F",  forms  the 
upper  end  of  the  column,  and  upon  these  the  mortar  is 
supported  as  follows  :  The  trunnion-carriage  G,  of  cast  steel, 
has  a  projecting  lug,  g' ,  through  which  passes  the  adjusting 
screw  K. 

The  lower  end  of  this  screw  bears  on  the  Belleville 
springs,  and  by  means  of  it  the  trunnion  carnages  may  be 
adjusted  till  the  mortar  is  in  the  proper  position  for  loading, 
and  it  is  then  secured  in  that  position  by  the  jam-nuts  k' . 

The  trunnion-carriages  G,  are  two  heavy  blocks  of  cast 
steel,  in  which  the  trunnions  rest,  and  which  slide,  under  the 


ARTILLERY   CARRIAGES— THEORY  OF  RECOIL. 


425 


force  of  recoil,  along  ways  planed  on  the  inner  side  of  the 
cylindrical  recess  E;  a  slot,  m,  Fig.  241,  being  left  in  the 

recess  for  the  projecting  lug  g'\ 
—K     a  section  of  the  trunnion-carriage 
~Z\    -,  »    and  recess  is  shown  in  Fig.  241. 

t  The  object  of  the  spiral  springs 
is  to  return  the  mortar  to  the  fir- 
ing position.  They  are  set  at  an 
angle  of  50°  with  the  horizontal, 
the  mortar  being  fired  between 
the  limits  35°  and  65°,  so  that  this 
is  a  mean  between  them.  To  ob- 
tain a  column  of  springs  of  suf- 
ficient length  to  return  the  piece 
—E  to  its  proper  position,  the  cylin. 
drical  recesses  in  the  cheeks  are 
lengthened  by  bolting  a  cylinder 
Ef,  Figs.  239  and  240,  to  the  bot- 
__  TT>  torn  of  E. 


F' 


-G 


241.  The   12-inch  Mortar  Carriage — 
Hydraulic  Buffers. 

Recoil  is  checked  by  two 
hydraulic  buffers,  H,  Figs.  239  and 
240,  one  on  each  side  of  the  car- 
riage, bolted  to  the  flanges  of  the 
cylindrical  recesses  E.  The  pis- 
ton-rods //,  Figs.  240  and  242,  of 
— E*  these  cylinders  are  attached  to 
the  lower  ends  of  the  trunnion- 
carriages  G.  When  the  piece  is 


FIG.   240. 


FIG.  241, 


426 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


fired,  the  spiral  springs  return  it  to  the  firing  position,  and 

hence  this  is  a  spring-return  carriage. 

The  arrangement  of  the  hydraulic  buffer  for  checking 
recoil  and  maintaining  a  constant  resist- 
ance in  the  cylinder,  differs  from  that 
for  the  8,  10,  and  1 2-inch  guns  as  fol- 
lows : 

A  channel,  A,  Fig.  242,  is  bored 
parallel  to  the  axis  of  the  cylinder  H. 
Holes,  a,  are  bored  at  different  intervals 
along  this  channel,  and  are  partially  or 
entirely  closed  by  screw-plugs,  b,  fitting 
into  the  holes  c.  These  plugs,  b,  are  of 
different  shapes,  so  that  they  will  either 
completely  close  the  openings  a,  when 
screwed  home,  or  will  leave  them  par- 
tially or  entirely  open.  They  are  never 
entirely  removed.  When  the  gun  re- 
coils, the  piston  moves  in  the  direction 
of  the  arrow,  Fig.  242.  At  the  first 
instant  of  recoil,  if  all  the  holes  a  are 
open,  it  is  evident  that  the  liquid  will  be 
forced  freely  through  these  holes,  and 
will  flow  along  the  channel  A,  and  return 
above  the  piston,  into  the  cylinder.  As 
the  motion  of  the  piston  continues,  each 
of  these  holes  will,  in  succession,  be  cut 
off,  and  the  flow  of  the  liquid  being  thus 
limited,  its  resistance  will  increase.  By 

partially  or  entirely  closing  the  holes  a,  it  is  evident  that 

any  resistance  to  flow,  within  limits,  may  be  obtained.     An 

equalizing-pipe,/,  connects  the  two  cylinders,  to  keep  the 

pressure  the  same  in  both. 

The  piston-rod  h! ,  passes  through  the  cylinder  at  both 

ends,  to   equalize  the   volumes,  and   the  piston-head,  s,  is 

solid. 

Its  upper  side  is  of  the  shape  shown,   and  the  upper 

cylinder-head,   s',  is   correspondingly   shaped.     When   the 

springs  return  the  piece  to  the  firing  position,  the  head  of 


FIG.  242. 


ARTILLERY   CARRIAGES— THEORY  OF  RECOIL. 


427 


the  cylinder,/,  enters  the  recess  in  the  piston-head, s,  and  by 
gradually  forcing  out  the  liquid,  the  counter-recoil  is 
checked,  and  the  piece  comes  into  the  firing  position 
without  shock.  Buffers,  £,  Fig.  240,  on  the  trunnion-car- 
riage also  avoid  this. 


242.  Remaining   Parts  of  the   12-inch  Mortar   Carriage — Roller- 
paths — Elevating-gear — Traversing-gear — Loading- scoop. 

ROLLER-PATHS. — In   the   8,    10,   and    1 2-inch   carriages, 
horizontal  motion  of  the  parts  is  prevented  by  the  central 
collar  or  pivot,  as  explained.     In  the    1 2-inch 
mortar   carriage,  as  the  recoil  of  the  piece  is 
downward,  the    central    part  of    the    carriage 
must  be   left  open,  and  hence  the  central  collar 
cannot     be    used.       Resistance    to    horizontal 
motion  is  therefore   obtained    by  forming  the 
upper   roller-path,  C,  so   that   it   overlaps   the 
lower  one,  A,  as  shown  in  Fig.  243,  which  is  a      FIG.  243. 
section  of  the  two.    Vertical  motion  is  prevented  by  the 
weight  of  the  system. 

ELEVATING-GEAR. — This  consists  of  a  bronze  toothed 
sector,  a,  bolted  to  the  mortar,  con- 
centric with  the  axis  of  the  trun- 
nions, into  which  works  a  gear,  b. 
A  large  gear,  c,  on  the  same  shaft  is 
driven  by  the  gear  d,  and  on  the  same 
shaft  with  d  is  a  hand-wheel,  e. 

The  gears  b,  c,  d,  and  the 
hand-wheel,  e,  are  all  mounted  on 
the  trunnion-carriage,  G,  and  as  the 
mortar  is  mounted  on  the  same 
carriage,  the  whole  elevating  device  recoils  together.  Each 
trunnion-carriage  carries  its  own  elevating-gear. 

TRAVERSING-GEAR. — This  consists  of  a  vertical  shaft,  a, 
Fig.  245,  attached  to  the  upper  carriage,  carrying  a  gear, 
b,  at  its  lower  end,  and  a  worm-wheel,  c,  at  its  upper 
end.  The  wheel,  b,  gears  into  a  toothed  ring,  d,  on  the 


FIG.  244. 


428 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


•a 


FIG.  245. 


inside  of  the  lower  roller-path,  and  the  shaft  is  rotated  by  a 
worm,  e,  driven  by  cranks,  /,  on  a  horizontal  shaft,  g,  passing 
through  the  front  of  the  cheeks  of  the 
top  carriage.  This  device  is  also  shown  in 
Fig.  239. 

For  pointing  in  azimuth,  a  cast-iron 
circle,  graduated  in  degrees,  is  fixed 
around  the  upper  roller-path,  and  a  pointer 
attached  to  this  path,  indicates  the  direc- 
tion. 

LOADING-SCOOP.  — This  consists  of  a 
scoop  or  tray,  a.  Fig.  239,  at  the  end  of  a 
lever,  b.  This  lever  is  pivoted  to  the  rear 
of  the  chassis  on  a  shaft,  c,  which  carries 
also  the  bent  lever  d.  The  outer  end  of 
this  lever  carries  a  nut,  e,  in  which  works 
the  screw,/.  This  screw  is  supported  in 
bearings  on  the  left  side  of  the  top  carriage,  and  extends  to 
the  front,  where  it  ends  in  a  hand- wheel, g.  By  turning  this 
hand-wheel,  the  scoop  is  raised  or  lowered,  carrying  the 
projectile  and  charge  to  the  breech  of  the  mortar. 

The  loading  position  for  the  mortar  is  an  elevation  of  5°. 

243.  Casemate  or  Turret  Carriages — General  Principles— Disappear- 
ing Carriages — General  Principles. 

GENERAL  PRINCIPLES  OF  TURRET  CARRIAGES.  -  -  The 
general  object  of  these  carriages,  is  to  secure  a  minimum 
height,  and  minimum  embrasure  opening.  Hence  the  cen- 
tre of  rotation  is  at  the  centre  of  the  embrasure,  and  the 
chassis  is  simply  a  pair  of  rails,  which  support  the  buffers 
carrying  the  gun. 

Elevation  is  given  by  lowering  or  raising  the  rear  ends 
of  the  rails,  and  direction  by  rotating  the  turret.  None  of 
these  carriages  have  as  yet  been  designed  for  the  land 
service. 

GENERAL  PRINCIPLES  OF  DISAPPEARING  CARRIAGES.— 
Owing  to  the  great  cost  of  modern  guns  and  carriages,  it  is 
important  to  protect  them  as  much  as  possible  from  injury 
from  fire.  This  may  be  done  either  by  placing  them  in 


ARTILLERY    CARRIAGES— THEORY   OF  RECOIL.         429 

armored  casemates  or  turrets,  or  in  gun-lifts,  or  by  using 
the  ordinary  barbette  battery,  and  placing  the  gun  upon  a 
disappearing  carriage.  The  great  cost  and  confined  space 
of  the  casemates,  turrets,  and  gun-lifts,  has  caused  the  adop- 
tion of  the  disappearing  type  of  carnages  in  exposed  sites. 

The  object  of  a  disappearing  carriage  is,  to  enable  the 
gun  to  be  fired  over  an  ordinary  parapet,  thus  giving  it  all 
the  advantages  of  an  extensive  field  of  view  and  of  fire, 
with  room  for  manoeuvre,  and  to  utilize  the  force  of  recoil 
in  returning  the  gun  to  cover  for  loading,  and  in  storing  up 
sufficient  energy,  during  recoil,  to  return  the  gun  to  the  firing 
position. 

There  are  therefore  two  points  to  be  especially  con- 
sidered : 

1.  The  means  of  checking  recoil,  so  that  the  gun  will  be 
covered  during  loading. 

2.  The  method  of  storing  up  energy  sufficient  to  return 
the  piece  to  the  firing  position. 

Checking  Recoil.  --  In  all  these  carriages,  the  gun  is 
mounted  at  the  ends  of  lever-arms,  and  these  arms  are 
pivoted,  in  various  ways,  to  the  chassis.  The  recoil  is 
checked  by  hydraulic  buffers,  or  in  some  cases  by  pneu- 
matic buffers,  which  allow  the  lever-arms  to  rotate  grad- 
ually to  the  rear,  bringing  the  gun  down  to  the  loading 
position. 

Return  to  Firing  Position. — The  energy  necessary  to 
return  the  gun  to  the  firing  position,  is  stored  up  in  various 
ways.  In  the  English  service,  a  hydro-pneumatic  buffer 
is  used ;  that  is,  the  liquid  which  is  forced  out  of  the 
hydraulic  cylinder,  by  recoil,  passes  into  an  air-chamber, 
and  compresses  the  air  sufficiently,  to  give  the  necessary 
pressure  for  returning  the  gun  to  the  firing  position,  as  soon 
as  a  valve  is  opened  between  the  air-chamber  and  the 
hydraulic  cylinder. 

Spiral  or  Belleville  springs  are  also  employed.  The 
recoil  is  checked  by  the  hydraulic  buffer,  and  the  springs 
restore  the  piece  to  its  firing  position. 

Counterweights  may  be  used,  either  alone,  or  in  connec- 
tion with  air  pressure. 


430 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


244.  Buffington-Crozier  Disappearing  Carriage. 

Two  successful  carriages  of  this  type  have  been  tried  in 
the  United  States,  and  an  outline  description  of  each  will  be 
given. 

BUFFINGTON-CROZIER. — This  carriage  was  designed  by 
Colonel  Buffington,  and  modified  by  Captain  Crozier,  both 
of  the  U.  S.  Ordnance  Department. 

The  carriage  consists  of  the  chassis,  A,  Fig.  246,  the  sup- 
porting levers,  £>,  carrying  the  gun,  the  hydraulic  buffers,  C, 
and  the  counterweight,  D.  The  carriage  is  a  front-pintle 
one.  The  gun  is  mounted  on  the  upper  ends  of  the  support- 


FIG.  246. 

ing  levers,  B.  These  levers  have  trunnions,  ^,  near  the  mid- 
dle, which  are  mounted  on  the  hydraulic  buffers,  C.  The 
lower  ends  of  the  levers  are  connected  by  a  cross-head  at  /, 
and  from  this  cross-head,  is  suspended  the  counterweight, 
D.  This  counterweight  rises  and  falls  vertically,  while  the 
trunnions,  e,  with  the  buffers,  move  horizontally  along  the 
chassis-rail,  a.  When  the  piece  is  fired,  the  force  of  recoil  is 
taken  up  by  the  buffers,  which  move  back  as  stated,  while 
the  counterweight,  D,  is  raised  vertically,  sliding  on  guides, 
g.  The  gun  in  the  loading  position  is  shown  at  G.  The 
counterweight  is  held  in  its  position  after  firing,  by  a  pawl, 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         43! 

//,  and  ratchet,  t,  which  being  released,  allows  the  weight  to 
descend,  and  thus  the  gun  is  raised  to  the  firing  position. 
The  trunnions  of  the  gun  describe  an  arc  of  an  ellipse  in 
their  descent.  The  bars  E  are  for  giving  elevation.  They 
are  attached  to  a  straight  rack,  b,  on  the  inside  of  the  chassis, 
which  is  worked  by  the  hand- wheel  c.  The  elevation  may 
be  given  in  either  the  loading  or  the  firing  position.  The 
carriage  rests  in  front  upon  a  ring  of  rollers,  F,  as  previously 
described,  and  is  traversed  by  the  chain,  d,  passing  over  a 
sprocket-wheel,  and  worked  by  a  crank. 

245.  The  Gordon  Disappearing  Carriage. 


FIG.  247. 


FIG.  248. 

This  carriage  was  designed  by  Capt.  Gordon  of  the 
U.  S.  Ordnance  Department,  and  consists  (Figs.  247  and 
248)  of  the  chassis  a,  the  top  carriage  b,  the  counterpoise  c, 
the  lever-arms  d,  the  hydraulic  cylinders  e,  and  the  air- 
chamber  f. 

The  chassis,  a,  is  a  heavy  casting,  supporting  all  the  parts, 
and  it  rests  when  in  the  firing  position  upon  a  platform. 
When  the  piece  is  to  be  moved  in  azimuth,  the  chassis  is 
supported  on  a  hydraulic  pivot,  not  shown  in  the  drawings, 


432 


TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 


by  which  arrangement  the  traversing  is  effected  with  very 
little  power. 

On  the  upper  side  of  the  chassis,  four  levers,  d,  are 
mounted,  two  of  them  being  shown  in  the  drawing. 

These  levers  rotate  about  the  axes,  g,  and  carry  at  their 
lower  ends,  a  heavy  counterweight,  c.  On  the  upper  ends 
of  these  levers  is  mounted  the  top  carriage,  £,  which  sup- 
ports the  piece.  A  hydraulic  cylinder,  e,  extends  along  the 
chassis. 

Its  piston  is  forced  in,  during  recoil,  and  the  liquid,  thus 
forced  into  the  air-chamber  f,  compresses  the  air,  and 
stores  up  the  energy  necessary  to  return  the  piece  to  the 
firing  position,  when  the  proper  valve  in  the  air-chamber 
is  opened.  The  trunnions  describe  an  arc  of  about  180° 
during  recoil,  thus  bringing  the  gun  close  to  the  parapet, 
and  affording  good  cover.  The  elevating  device  is  attached 
to  the  top  carriage.  This  is  a  centre-pintle  carriage. 

Several  disappearing  carriages  are  in  use  abroad,  as  the 
Moncreiff,  Armstrong,  Canet,  etc. 

246.  Old  Seacoast  Carriages  in  II.  S.  Service. 

Certain  old  carriages  are  still  retained  in  the  U.  S.  ser- 
vice for  the  8-inch  converted  rifles,  and  the  1 5-inch  Rodman 
smooth-bore  guns.  They  consist  (Fig.  249)  of  a  chassis,  a,. 
and  a  top  carriage,  b,  made  of  wrought  iron. 


FIG.  249. 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         433 

The  chassis  is  composed  of  two  parallel,  I-shaped  rails, 
connected  by  transoms,  and  attached  to  it,  between  the  rails, 
is  the  hydraulic  buffer,  c.  The  piston  of  this  buffer  is  at- 
tached to  the  top  carriage  by  a  lug,  d,  on  the  latter.  The 
buffer  itself,  is  one  of  constant  orifice,  and  variable  resistance, 
as  will  be  explained.  Bolted  to  the  rear  end  of  the  chassis- 
rail,  is  an  inclined  rail,  e.  The  retraction  gear  is  shown  at/. 
The  principle  of  this  carriage  is  as  follows : 
When  the  piece  is  fired,  the  top  carriage  rests,  through- 
out its  length,  upon  the  chassis-rail,  and  hence  the  force  of 
recoil  is  distributed  over  this  length,  and  the  top  carriage 
starts  to  the  rear  on  sliding  friction.  After  a  very  small 
movement  in  recoil,  the  wheel, g,  of  the  top  carriage  (Fig.25o), 
strikes  the  wedge-shape  drail,  e,  and  begins  to  rotate.  This 
causes  the  top  carriage  to  tip  slightly  forward,  and  brings 


FIG.  250. 

the  front  wheel,  h,  into  bearing  on  the  chassis-rail.  The  car- 
riage then  moves  on  rolling  friction.  The  result  of  this 
arrangement  is,  that  the  top  carriage  rests,  throughout  the 
recoil,  on  rolling  friction,  as  shown  Fig.  250.  A  spring  pawl 
and  ratchet,  retain  the  top  carriage  in  the  loading  position, 
after  recoil,  and  by  releasing  the  pawl,  the  top  carriage 
returns  on  rolling  friction  to  its  firing  position,  by  gravity. 

For  drill  purposes,  to  bring  the  gun  from  battery,  for 
loading,  the  rear  wheel,  g,  is  mounted  on  an  eccentric  axle, 
and  when  thrown  into  bearing  against  the  chassis-rail,  by  the 
action  of  a  handspike,  it  tips  the  top  carriage  forward,  and 
brings  the  front  wheel,  //,  also  into  bearing.  The  piece,  and 
top  carriage,  are  then  drawn  to  the  rear,  by  a  rope  attached 
to  the  latter  (Fig.  249),  and  wound  round  a  drum  on  the  shaft 
of  the  retraction  gear/. 


434  TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 

THEORY   OF   RECOIL. 

247.  Maximum  Velocity  of  Recoil. 

The  velocity  of  recoil  at  the  instant  the  projectile  leaves 
the  muzzle  is  given  by  equation  65,  Interior  Ballistics.  This 
does  not  represent  the  maximum  velocity  of  recoil,  however, 
for  the  reasons  stated,  and  a  new  equation  is  necessary  to 
determine  this  velocity. 

In  equation  65,  it  is  assumed,  that  the  mean  velocity  of 
the  particles  of  the  charge,  is  one  half  that  of  the  velocity  of 

the  projectile;  that  is,  the  equation  contains  the  termf— v\ 

in  which  c3  is  the  weight  of  the  charge,  and  v  the  velocity  of 
the  projectile. 

This  is  very  nearly  true  while  the  projectile  is  in  the 
bore,  because  the  layer  of  gas  next  the  projectile  has  the 
same  velocity  as  the  latter,  and  this  velocity  decreases  to 
zero,  for  the  layers  toward  the  bottom  of  the  bore. 

But  when  the  projectile  leaves  the  muzzle,  this  condition 
no  longer  exists.  The  gases,  which  were  before  confined, 
rush  out  with  greatly  increased  velocity,  and  this  affects 
the  recoil  of  the  piece. 

Let  P  denote  the  weight  of  gun,  and  part  of  the  carriage 

which  recoils ; 

p,  the  weight  of  the  projectile ; 
c3,  the  weight  of  the  charge ; 
Vm',  the  maximum  velocity  of  recoil; 
V,  the  initial  velocity  of  the  projectile ; 
vm,  the  mean  of  the  maximum  velocities  of  the  powder- 
gas  upon  issuing  from  the  piece. 
Then  the  equation 

Pr*!=pV+&vm (335) 

expresses  the  equality  of  momenta  of  the  piece,  projectile, 
and  charge  at  this  instant. 

General  Sebert  of  the  French  Artillery,  has  determined 
with  his  velocimeter,  previously  described,  that  in  order  that 
the  above  equation  be  true,  the  value  vm  must  be  about  3000 
ft  -sees. 


ARTILLERY  CARRIAGES—  THEORY  OF  RECOIL.         435 

Hence  the  maximum  velocity  of  recoil  is  given  by 

Vml=tV±£***t    .....    (336) 

while  the  velocity  of  recoil  during  the  time  the  projectile  is 
in  the  bore  is  (equation  65) 

,    & 

pv  +  -v 


248.  Periods  of  Recoil—  Relation    between    Time,  Velocity,    and 
Length  of  Recoil  in  First  Period. 

PERIODS.  —  The  recoil  of  a  gun  is  divided  into  two 
periods  : 

1.  From  the  time  the  gas  begins  to  act,  until  the  maximum 
velocity  of  recoil  is  attained. 

2.  From    the  end   of   the  first  period,  till  the   piece   is 
brought  to  rest. 

RELATIONS  BETWEEN  TIME,  VELOCITY,  AND  LENGTH  OF 
RECOIL  IN  FIRST  PERIOD.  —  In  order  to  determine  the  cir- 
cumstances of  recoil  in  the  first  period,  it  is  necessary  to 
know  the  relations  between  the  time,  velocity,  and  length  of 
recoil,  and  these  are  determined  in  the  following  manner: 

If  the  distance  recoiled  by  the  piece,  at  the  end  of  any 
time  /,  be  denoted  by  x,  the  velocity  at  that  time  is 

dx 
"-*> 

and  the  distance  x  passed  over  is 

'v'dt. 


=/< 


Hence,  considering  the  expression  /  v'dt,  if  we  con- 
struct a  curve  whose  abscissas  are  the  values  of  /,  and  whose 
ordinates  are  the  corresponding  values  of  v' ,  this  curve 
will  be  of  the  form  Fig.  251,  and  from  it  we  deduce  the  fol- 
lowing laws : 

i.  The  velocities  of  recoil  increase  very  rapidly  at  first, 
till  the  point  of  inflection  i  is  reached,  and  then  more  slowly, 


43^ 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


till  they  cease  to  increase  at  the  time  corresponding  to  the 
maximum  velocity  F,/,  which  time  is  denoted  by  r. 

2.  The  area  included  between  the  curve,  the  axis  T,  and 
any  ordinate  v',  is  the  distance  x  passed  over  in  recoil,  at 

the  time  t  corresponding-  to  that  ordinate,  since  x  —  /  v  'dt ; 

and  the  total  length  of  recoil  during  the  first  period  is  the 
area  corresponding  to  the  ordinate  r. 

This  curve  was  constructed  by  experiment,  by  obtaining 
with  the  Sebert  velocimeter,  the  values  of  vf  corresponding 
to  different  values  of  t. 


249.  Ordinary  Case — Steps  in  the  Solution  of  the  Problem. 

In  the  case  just  considered,  the  relations  between  the 
velocities  of  recoil  v ',  and  the  corresponding  times  /,  were 
determined  by  experiment. 

ORDINARY  CASE. — Ordinarily,  this  relation  between  v ' 
and  t  is  not  known.  It  may,  however,  be  determined  by  a 
series  of  steps  as  follows : 

STEPS. — We  have  the  relation  between  the  velocity  of 
the  projectile  v  and  the  length  of  its  travel  u  in  the  bore, 
by  Sarrau's  monomial  or  binomial  formulas;  hence  we  have 
a  relation  v  =/(u). 

i.  We  next  determine  the  time  t  required  for  the  projec- 
tile to  pass  over  any  length  of  bore  u.  This  gives  a  relation 


ARTILLERY  CARRIAGES— THEORY   OF  RECOIL. 


437 


2.  Combining  the  curves  v  =  f(u)  and  t  =/(«),  we  de- 
termine the  relation  v  =.f(f). 

This  is  done  by  using  the  ordinates  of  the  time  curve 
/  =f(u)  as  abscissas,  and  those  of  the  velocity  curve  v  =f(u) 
as  ordinates,  and  constructing  a  curve  whose  equation  is 
«/=/(/).  This  equation  gives  the  relation  between  the 
velocity  of  the  projectile,  and  the  corresponding  time  /. 

3.  To  pass  from  this  curve  to  that  of  the  velocity  of  re- 
coil as  a  function  of  the  time  t,  we  have  equations  (65)  and 
(336),  giving  the  relation  at  any  time  t  between  the  velocity 
of  the  projectile  and  that  of  the  piece;  and  knowing  that  of  the 
projectile  we  may  at  once  find  that  of  the  piece  as  a  function 
of  the  time,  or  v'  =f(i),  which  is  the  curve  required. 

V 


0 


FIG.  252. 

Having  the  curve  v '  =  /(/),  we  can  determine,  as  pre- 
viously shown,  the  time,  and  length  of  recoil,  corresponding 
to  any  given  velocity. 

250.  First  Step— Time  of  Passage  of  Projectile  over  a  Given  Length 
of  Bore — Difficulty — Remedy. 

Assuming  the  binomial  and  monomial  formulas  (91)  and 
(121),  Interior  Ballistics,  we  apply  the  one  which  is  suitable 
to  the  particular  case  under  consideration,  and  construct 
the  curve  whose  abscissas  are  the  values  of  u,  and  its  ordi- 
nates the  corresponding  values  of  v.  This  curve  will  be  of 
the  form  Fig.  252. 

The  value  for  the  velocity  at  any  point  u  is,  from  calculus, 

du 


dt' 


43 8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

from  which  we  have 

1-    *L 

v  ~~  du 

Multiplying  by  du  and  integrating,  we  have 


or 


FIG.  253. 

Hence  if  we  construct  a  curve  whose  abscissas  are  the 
values  of  u,  and  its  ordinates  the  corresponding  values  of  — , 
the  area  included  between  this  curve,  the  axis  of  u,  and  any 
ordinate  —  will  give  for  any  value  of  u  the  time  t  required 

for  the  projectile  to  pass  over  this  distance  u  in  the  bore. 
The  form  of  this  curve  is  shown  in  Fig.  253. 
DIFFICULTY.— The  only  difficulty  in  this  case  is  that  for 

very  small  values  of  v  the  ordinates  —  will  be  large,  and  will 

not  fall  within  the  limits  of  an  ordinary  drawing,  and  hence 
the  area  under  the  curve  cannot  be  accurately  measured, 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL. 


439 


and  therefore  the  time  corresponding  to  a  given  travel  u 
cannot  be  exactly  ascertained. 

REMEDY. — To  obviate  this  difficulty,  we  assume  (as  is 
nearly  correct)  that  the  velocity  of  the  projectile,  as  a 
function  of  the  time  varies  nearly  as  the  abscissas  and 
ordinates  of  a  common  parabola,  whence  we  have 


V  =        2pt 

Multiplying  by  dt  and  integrating,  we  have 
I   vdt  =    I  -jjrdt  =  u  =    I   J~2ptdt  = 


(337) 


(338) 


FIG.  254. 


At  the  instant  the  shot  leaves  the  bore,  v  in  equation 
(337)  becomes  the  initial  velocity  V.  Denoting  the  cor- 
responding time  by  t ' ,  we  have,  equation  (337), 

—         V 


and  this  value  of  -\/2p  in  equation  (338)  gives 

'.=  !£' (339) 

u  being  the  total  length  of  travel  of  the  projectile.     Com- 


440 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


paring  this  total  time  of  passage  of  the  projectile  through  the 
bore,  with  that  obtained  from  that  part  of  the  area  under  the 
curve  of  reciprocals  which  can  be  measured,  the  value  of 
the  unmeasured  portion  can  be  ascertained  very  nearly. 
Thus  the  relation  t  =  f(u)  is  determined  and  the  curve  is 
given  in  Fig.  254. 

251.  Second  and  Third  Steps  in  Determining  the  Curve  of  Velocity 
of  Recoil  as  a  Function  of  the  Time. 

SECOND  STEP. — Taking  the  ordinates  of  the  curve 
t  —  f(u]  as  abscissas,  and  those  of  the  velocity-curve 
v  =f(u)  as  ordinates,  we  construct  a  curve  v  =f(t),  showing 
the  relations  between  the  velocity  of  the  projectile  and  the 
corresponding  time,  and  this  curve  will  be  of  the  form 
shown  in  Fig.  255. 


FIG.  255. 


THIRD  STEP  —  RELATION  BETWEEN  VELOCITY  OF  PRO- 
JECTILE AND  THAT  OF  RECOIL.—  We  have  for  the  velocity 
of  recoil  of  the  piece  and  carriage  while  the  projectile  is  in 
the  bore,  equation  (65), 


and  for  the  maximum  velocity  of  recoil,  equation  (336) 


V  '  — 

v  m     — 


pV  +  3QOO&? 


ARTILLERY   CARRIAGES—  THEORY   OF  RECOIL.         44! 

Since  v  is  determined  as  a  function  of  t  by  the  second 
step,  v'  may  be  found  for  the  corresponding  times  by 
^equation  (65),  by  multiplying  the  ordinates  of  the  curve  just 


•determined,  Fig.  255,  by  the  ratio    -  f      .     A  curve  can 

then  be  constructed,  similar  to  that  in  Fig.  255,  giving  the 
velocities  of  recoil  of  the  piece,  for  each  instant  of  the 
passage  of  the  projectile  through  the  bore,  and  the  area 
under  this  curve,  bounded  by  the  axis  of  T  and  any 
•ordinate  v'  will  give  the  corresponding  space  passed  over, 

since  Cv'dt  —  x. 

After  the  projectile  quits  the  bore,  equation  (65)  no 
longer  applies;  but  it  is  known  that  the  curve  becomes 
tangent  to  a  line  parallel  to  the  axis  of  T,  at  a  point  given 


FIG.  256. 

by  equation  (336),  and  it  is  reasonable  to  infer,  that  the  rate 
of  curvature  of  the  curve  of  recoil,  will  continue  uniform  up 
to  this  point  of  tangency. 

Hence,  drawing  a  line  parallel  to  the  axis  of  T,  at  the 
distance  given  by  equation  (336), 


77  /  _- 

*  m     — 


and  continuing  the  curve  already  drawn,  preserving  its  gen- 
eral rate  of  curvature  up  to  this  line,  we  have  the  curve 


442 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


v'  =  /(/),  giving-  the  time  and  space  passed  over  in  recoil, 
and  this  curve  will  be  of  the  form  Fig.  256. 

252.  Example— 8-inch  Steel  B.  L.  Rifle— First  Step— Curve  t  —f(u}. 

For  example  take  the  case  of  the  8-inch  Steel  B.  L.  Rifle. 
The  velocity  curve  for  this  gun,  with  125  pounds  brown 
powder,  is  given  in  Fig.  257. 


v 


.u 


FIG.  257 


From  it  we  obtain  the  following  abscissas  and  ordinates 


u  (Feet). 

0.46 . . 

1.70.. 
2.40 . . 
3.20.. 
3.70.. 
7.30.. 
9.50.. 

11.50. . 
13.00. . 

14.30.. 
15.75,. 


z/ (Foot-seconds). 


387 

935 
1080 
1197 
1259 

1545 
1655 
1727 

1787 
1827 
1859 


1743 -• 1884  I.  V. 

From  which  we  have  the  following  values  of  — ,  and  the 
curve  of  reciprocals,  Fig.  258. 


ARTILLERY  CARRIAGES— THEORY   OF  RECOIL. 

u  (Feet).  I. 

v 

0.46 002584 

I./O OOI069 

2.4O , 0009259 

3-20 0008354 

370  • 0007943 

7.30 0006472 

9.50 0006042 

11.50 0005790 

1 3.00  0005  596 

14-30 0005473 

15-75 0005379 

1743 - 0005308 


443 


FIG.  258. 

For  the  total  time  of  passage  of  the  projectile  through 
the  bore  we  have,  using  the  area  of  the  parabola  (eq.  339), 


Hence  the  total  area  under  the  curve  of  reciprocals 
should  be  nearly  .01387  second. 

In  the  absence  of  a  more  accurate  method,  the  area  under 
the  curve,  which  can  be  measured,  may  be  obtained  by  con- 
sidering each  portion  of  the  area  bounded  by  the  curve,  the 


444  TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 

axis  of  u,  and  the  two  adjacent  ordinates,  as  a  trapezoid,  and 
finding  its  area. 

Thus  for  the  first  trapezoid  we  have 

(  .002584 
ordinates  \ 

{  .001069 

Value  of  u  =  1.24  —  1.70  —  0.46. 

.         /.oo2  5  84  +  .00 1 069^ 
Area  (—         — ! —         — j  X  1.24  =  .00227  sec. 

Following  this  method,  we  have  the  table: 

/P      •,  Successive  Successive  times,  Total  times, 

differences.  seconds.  seconds. 

0.46  o 

1.70...--...  1.24 OO227 .OO227 

2.40 0.70 0006979 0029679 

3.20. 0.80 000704 0036719 

370 0.50 0004075 0040794 

7.30 3-60 002592 0066714 

9.50 2.20 001386 0080574 

II.5O 2.OO ,..  .OOIl8o 0092374 

13.00 1.50 000854 OI009I4 

14.30 1.30 000715 0108064 

15.75 i-45 000787 0115934 

17.43 1-68 000897 0124904 

From  this  table  we  can  obtain  the  time  of  travel  of  the 
projectile  over  any  distance  u. 

The  sum  of  the  times  is  .01249  second,  while  the  total 
time  is,  as  above  shown,  .01387  second. 

Hence  the  difference,  .00138  second,  is  the  area  that  can- 
not be  measured. 

253.  Examples— Second  and  Third  Steps. 

The  table  on  page  442  gives  the  curve  v  —  f(u),  that  on 
this  page  the  curve  t  =/(«).  Taking  the  ordinates  of  the 
latter  curve  as  abscissas,  and  those  of  the  former  as  ordi- 
nates, we  can  form  the  following  table,  whose  abscissas  and 
ordinates  are  those  of  the  curve  v  =f(t): 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         445 

Total  Successive  times,  Ordinates. 

times,  t.  seconds.  Velocities  foot-seconds,  v. 

O                                               O 
.00138.... 00138 387 

.00365 00227 935 

.00435 000698 1080 

.00505 .000704  1197 

.00546 0004075 1259 

.00805 002592 1545 

.00944 OOI386 1655 

.01062 OOIlSO 1727 

.OII47 OOO854 1787 

.01219 000715 1827 

.01297 000787 1859 

.01387 000897 1884 1.  v.; 

and  from  this  we  construct  the  curve  of  velocities  of  the 
projectile  as  a  function  of  the  times.  Passing  to  the  consid- 
eration of  the  recoil  of  the  piece  and  carriage,  we  have, 
equation  (65), 


p  =  300  Ibs. ; 
&  —-  125  Ibs. ; 
P  =  1 8  tons  =  40320  Ibs. 
Hence 

v'  =  .00899^  =  .009^. 

From  this  formula,  having  the  values  of  v  and  the  corre- 
sponding times  /,  we  can  form  the  following  table  and  con- 
struct the  curve  of  recoil  of  the  piece  and  carriage  as  a 
function  of  the  time. 

Velocity  of  recoil  of 

Total  times,  Piece  and  Carriage, 

seconds.  foot-seconds. 

0.0000 
.00138 3-483 

.00365 , 8.41 5 

•00435 9720 

.00505    10.773 


44-6           TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 
.00546 H.33I 

.00805 1 3-9°5 

•00944 14-895 

.01062    I5.56I 

.OI  147 16.083 

.OI2I9 16.453 

.01297 16.73  I 

.01387 16.956 

From  equation  (336)  the  maximum  velocity  of  recoil  is 


'  =  23.32  ft.-seconds. 


H- .01387 


FIG.  259. 


From  the  above  data  the  curve  of  recoil,  Fig.  259,  may 
be  constructed. 

Drawing  a  line  parallel  to  the  axis  of  T,  at  the  distance 
Vmf  =  23.32  ft.-secs.,  this  line  will  mark  the  limit  of  accelera- 
tion. 

From  this  curve,  the  time  corresponding  to  any  velocity 
of  recoil  can  be  obtained,  and  the  area  under  the  curve  will 
give  the  corresponding  space  passed  over. 

254.  Problems. 

i.  Required  the  time  at  which  the  velocity  of  recoil  is 
13.905  ft.-sec. 


ARTILLERY    CARRIAGES— THEORY  OF  RECOIL.         447 

The  table  page  446  shows  it  to  be  .00805  second. 

2.  Required  the  space  passed  over  in  recoil  at  the  end  of 
this  time. 

It  will  be  the  area  under  the  curve,  from  the  origin,  up 
to  the  ordinate  whose  value  is  13.905  ft.-secs.,  or,  approxi- 
mately, the  sums  obtained  by  adding  the  separate  areas 
regarded  as  trapezoids,  up  to  this  point.  As  an  approxima- 
tion to  the  true  result,  regard  the  curve  as  a  parabola.  The 
result  thus  obtained  will  be  slightly  too  great.  The  area 
under  the  curve  will  be  two  thirds  the  rectangle  of  the  ab- 
scissa and  ordinate  of  any  point. 

Hence  for  the  area  in  question  we  have 

s  =  -  X  .00805  X  I3-905  =  -0746  ft.  =  .895  inches. 
«j 

3.  Required  the  space  passed  over  by  the  gun  and  car- 
riage at  the  time  the  projectile  leaves  the  bore. 

By  the  same  method  of  approximation  we  have 

s  =  -  X  -01387  X  16.956  =  .1567  ft.  =  1.88  inches, 
o 

4.  Required  the  time  at  which  the  velocity  of  recoil  is  a 
maximum,  and  the  space  passed  over  at  this  time. 

The  curve  v'  =  f(t)  gives,  by  measurement,  for  the  value 
of  t  =  .0395  seconds. 

The  space  passed  over  will  be  approximately 

s  =  -  X  .0359  X  23.32  =  .558  ft.  =  6.70  inches. 

In  the  same  way  all  the  circumstances  of  the  recoil  of  a 
gun  during  the  first  period,  may  be  obtained,  having  the 
curve  v  =  f(u),  which  can  be  obtained  from  Sarrau's 
formulas. 

255.  Time  and  Length  of  Recoil  in  Second  Period. 

TIME  OF  RECOIL. — At  the  beginning  of  the  second 
period,  the  acceleration  is  zero,  and  the  gun  and  carriage 
have  acquired  the  maximum  velocity  of  recoil  Vmr.  For 
simplicity  of  discussion,  suppose  the  chassis  horizontal. 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  only  force  acting  during  the  second  period  is  friction,, 
and  this  being  practically  constant,  will  uniformly  retard 
the  carriage  and  piece,  till  they  are  brought  to  rest. 
Let/  be  the  coefficient  of  friction  =  0.2  about; 
y  the  retardation  due  to  friction  ; 
P  the  weight  of  the  gun  and  carriage  which  is  mov- 
ing in  recoil ; 

M the  mass  of  the  moving  parts; 
V"  the  velocity  of  recoil  at   any  time   t   during  the 

second  period. 
Then  from  mechanics 

dV"          fP 
r  =  -*-  =  —M (340) 

The  velocity  at  any  time  t  during  the  second  period  will 
be,  from  (340), 


When  t  =  o,  or  at  the  beginning  of  the  second  period, 
V"  =  Vm'  \  hence  in  (341)  we  have 

V"=^-Wf-   ......     (342) 

At  the  end   of  the  second    period,  when   recoil  ceases, 
V"  =  o,  and  the  corresponding  time  is,  from  (342), 


n        VJ 

~r=~  .......  (343) 


LENGTH  OF  RECOIL.  —  Assuming  equation  (342),  we  have 
for  the  length  of  recoil,  at  the  end  of  any  time,  /,  in  the  second 
period 


__ 

dt~  "       M' 

v"dt=vmdt-tdt.     .     (344) 


ARTILLERY   CARRIAGES—  THEORY   OF  RECOIL.         449 


s  = 


(345) 


At  the  end  of.recoil  we  have  for  the  value  of  t,  from  (343), 


V 

rr>  111 

~'~~' 


Substituting  this  value  of  /  in  (345)  gives 


but 


V  ' 2      i  fP  V  ' ' 

¥-i:f^= (346) 


hence  in  (346) 


(347) 


FIG.  260. 

256.  Curve  Representing  Total  Recoil— Application  to  8-inch  Rifle. 
Second  Period. 

CURVE  OF  TOTAL  RECOIL.— The  curve  representing  all 
the  circumstances  of  recoil  of  the  piece  and  carriage,  will  be 
obtained,  by  combining  that  for  the  first  period,  with  the 
right  line  representing  the  second  period,  and  will  be  of  the 
form  Fig.  260. 

APPLICATION  TO  S-INCH  RIFLE. 

i.  Required  the  time,  from  the  beginning  of  the  second 
period,  at  which  the  velocity  of  recoil  will  be  10  ft.-secs., 
and  the  space  passed  over  at  that  time . 

From  (342), 

10  =  23.32  — .2  X  32.2  X/; 


45°  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

t  =  2.068  seconds  ; 
from  (345), 

s  =  23.32  X  2.068  —  i  X  .2  X  32.2  X  (2.o68)2; 
s  =  34.46  feet. 

2.  Required  the  time  from  the  beginning  of  the  second 
period  to  the  end  of  recoil,  and  the  total  space  passed  over 
in  recoil : 

From  (343), 

23.32 

-  =  3.621  seconds. 


32.2  X  .2 

From  (347), 

s  =  — -  —  ^ —  42.22  feet. 

2  X  32.2  X  -2 

In  a  similar  manner,  all  the  circumstances  of  the  recoil 
during  the  second  period  can  be  obtained,  having  the  value 
of  Vm'  from  formula  (336).  i 

257.  Wheeled  Carriages — Cases. 

The  preceding  discussions  relate  to  carriages  which  slide 
in  recoil,  such  as  those  for  seacoast  guns. 

For  wheeled  carriages  two  cases  may  arise : 

1.  The  carriage  may  recoil,  the  wheels  rotating,  and  not 
leaving  the  ground  or  platform  upon  which  they  rest. 

2.  The  wheels  may  leave  the  ground  or  platform,  depend- 
ing upon  the  relative  values  of  the  components  of  the  force 
of  recoil  which  act  to  produce  translation  and  rotation. 

In  the  second  case,  the  phenomenon  of  recoil  is  composed 
of  alternate  periods,  during  which  the  wheels  rise,  and  return 
again  to  the  platform. 

If  the  carriage  slides  in  recoil,  with  the  wheels  always  in 
contact  with  the  ground,  the  preceding  discussions  apply, 
the  only  change  necessary  being  a  decrease  in  the  value  of 
the  coefficient  of  friction,  due  to  the  lubrication  of  the  bear- 
ing surfaces  of  the  nave  and  axle-arm.  The  coefficient,  /,  in 
this  case  is  decreased  to  about  two  thirds  its  ordinary  value. 

If  the  wheels  rise,  increased  pressure  is  produced  on  the 
trail.  This  increased  pressure,  decreases  the  extent  of  recoil 


ARTILLERY    CARRIAGES— THEORY   OF  RECOIL. 


451 


•as  compared  with  that  which  obtains  in  the  first  case,  and  hence 
the  values  for  time,  velocity,  and  length  of  recoil  deduced  for 
the  first  case,  will  be  greater  than  those  for  the  second.  As  the 
calculations  in  the  second  case  are  somewhat  complicated, 
those  for  the  first  case  may  be  used  instead  of  them,  as  being 
safe  in  practice. 

258.  To  Calculate  the  Angle  of  Elevation  of  the  Piece  for  which  the 
Wheels  will  Rise. 

The  rotation  of  the  carriage  about  the  trail,  depends  on 
the  angle  of  elevation  at  which  the  piece  is  fired.  There  is 
a  limiting  angle  for  which  this  rotation  will  occur.  For  all 


7 


D  I 

FIG.  261. 


angles  greater  than  this,  rotation  will  not  occur,  and  for  all 
angles  less  than  this,  it  will  always  occur.  It  is  required  to 
determine  this  limiting  angle. 

Let  OM,  Fig.  261,  be  the  axis  of  the  piece,  and  the  line 
of  action  of  the  force  P0 .  Resolving  this  force  into  its  com- 
ponents parallel  and  perpendicular  to  the  ground,  we  have 

OE  =  PQ  cos  ot ; 
ON  =  P0  sin  a. 

With  reference  to  the  point  C,  the  component  OE  acts 
with  a  lever-arm  OD  to  raise  the  wheels,  while  ON  acts 
with  a  lever-arm  DC  to  keep  them  in  contact  with  the 


45  2  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

ground.  Let  G  be  the  centre  of  gravity  of  the  system,, 
composed  of  gun  and  carriage. 

Then  the  weight  P  acts  at  G,  with  a  lever-arm  CI,  to 
keep  the  wheels  down.  In  addition  to  these,  the  system 
moves  under  the  action  of  the  force  OE  with  an  accelera- 
tion y,  and  hence  its  force  is  My,  and  this  force  diminishes 
the  rotative  effect  of  the  force  OE,  since  the  action  of 
this  force  OE,  is  to  produce  both  rotation  around  C,  and 
translation  along  CD. 

This  latter  force,  My,  has  a  lever-arm  GL  We  have 
therefore,  calling  those  forces  which  tend  to  cause  a  lifting 
of  the  wheels  positive,  and  those  which  oppose  it  negative, 

+  OE,  lever-arm  OD  ; 

-  ON,          "  DC; 

-  P,  "  CI; 

-  My,          "  GL 

When  the  sum  of  the  moments  of  these  forces  with 
respect  to  C  is  zero,  the  wheels  will  be  on  the  point  of 
leaving  the  ground. 

Hence  this  gives  the  condition  required. 

Making 


we  have 

+  P.  cos  a  .  a  —  P0  sin  a  .  d  —  P  .  b  —  Myh  =  o.    (348) 

The  value  of  y  is  obtained  as  follows  :  Denoting  the 
total  pressure  of  the  powder-gas  by  P0  ,  the  component  of 
this  pressure  causing  recoil  is  P9  cos  a.  This  force  is  opposed 
by  the  friction  due  to  the  component  P0  sin  a  and  the  weight 
of  the  gun  and  carriage  P.  Hence  the  force  opposing 
motion  isf(P0  sin  a  -f-  P). 

From  mechanics  we  have  therefore  for  the  acceleration 

X  =  -i[/>0  cos  a-f(P,  sin  «  +  />)].    .     .     (349) 


ARTILLERY   CARRIAGES—  THEORY  OF  RECOIL.         453 

Substituting  this  value  for  y  in  (348),  which  can  be  done, 
since  the  wheels  are  just  about  to  leave  the  ground,  and 
therefore  the  case  is  one  of  horizontal  sliding,  we  have 

P.  cos  a(a  -  k)  -  PQ  sin  a(d  -  fh)  -  P(b  -  fh)  =  o.  (350) 

Now  making  P  —  o  in  comparison  with  P0,  and  calling 
<x0  the  value  of  a  for  this  limit,  where  the  wheels  are  just 
quitting  the  ground,  we  have 

a-h 
0  =     _,  ......     (351) 


in  which  a  and  d  can  be  found  by  direct  measurement  of 
the  gun  and  carriage,  and  the  centre  of  gravity  by  suspend- 
ing the  system  in  two  different  positions,  and  noting  the 
point  of  intersection  of  the  lines  of  suspension  when  pro- 
duced. 

BRAKES   AND   BUFFERS. 

259.  Necessity  for  Means  of  Checking  Recoil  —  Conditions  which  a 
Good  Brake  should  Fulfil—  Classes. 

NECESSITY  FOR  MEANS  OF  CHECKING  RECOIL.—  The 
above  discussion,  and  its  application  in  the  case  of  the  8-inch 
gun,  show,  that  unless  some  artificial  means  be  employed 
to  check  recoil,  its  extent  will  be  so  great  as  to  cause 
inconvenience. 

This  is  especially  true  with  modern  field,  siege,  and 
seacoast  guns,  where  the  weights  and  initial  velocities  of 
the  projectiles  have  greatly  increased,  without  a  correspond- 
ing increase  in  the  weight  of  gun  and  carriage,  and  hence 
the  length  of  recoil  has  been  greatly  increased. 

In  the  field  and  siege  services,  this  entails  great  fatigue 
upon  the  cannoneers  in  running  the  gun  and  carriage  back 
to  battery,  with  a  consequent  delay  in  firing,  and  exposure 
to  the  enemy's  fire. 

In  the  seacoast  service,  the  length  of  recoil  must  be 
limited  to  three  or  four  calibres,  on  account  of  cover,  as  the 
guns,  if  mounted  in  turrets,  or  similar  places,  have  very  lim- 
ited space  for  working;  and  if  mounted  in  barbette,  a  long 


454  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

recoil  exposes  the  gun  to  hostile  fire,  and  increases  the  time 
between  shots.  For  these  reasons,  brakes  or  buffers  are 
employed  with  modern  guns. 

CONDITIONS  WHICH  A  GOOD  BRAKE  SHOULD  FULFIL.— 
A  good  brake  or  buffer  should  fulfil  the  following  conditions  : 

1.  Its  resistance  should  be  constant  at  all  times. 

2.  For  the  same  piece,  charge,  and  projectile,  the  length 
of  recoil  should  always  be  the  same,  which  is  a  proof  of  the 
regularity  of  its  action. 

3.  It  should  be  entirely  automatic. 

4.  Its  line  of  resistance  should  be  as  nearly  as  possible  in 
the  line  of  action  of  the  force  producing  recoil,  so  as  to  avoid 
an  overturning  moment;  and  it  must  not  interfere  with  the 
movement  of  the  gun  to  and  from  battery,  and  its  manoeu- 
vring. 

CLASSES. — Brakes  are  divided  into  two  general  classes: 

1.  Friction  brakes. 

2.  Hydraulic  brakes. 

260.  Friction  Brakes  for  Seacoast  Carriages — Objections. 

The  various  friction-brakes  for  field  and  siege  carriages, 
have  already  been  explained.  Those  for  seacoast  carriages 
consist  generally  of  a  series  of  plates,  fixed  to  the  chassis, 
between  each  pair  of  which,  slides  a  plate  attached  to  the 
top  carriage.  The  plates  are  so  arranged,  that  by  means  of 
a  screw  or  other  device  they  may  be  pressed  together,  and 
the  friction  due  to  this  pressure  limits  the  recoil. 

Let  P9  represent  the  pressure  at  each  surface  in  contact ; 
ny  the  number  of  surfaces  ; 
S,  the  length  of  recoil  in  second  period ; 
f,  the  coefficient  of  friction  ; 
P,  the  weight  of  gun  and  carriage  recoiling ; 
Vm',  the  maximum  velocity  of  recoil  with  brake  acting. 
Suppose  the  chassis  horizontal ;  then  the  work  of  fric- 
tion of  the  plates,  plus  that  of  the  piece  and  carriage,  over 
the   path  S,  will  be  equal  to  the  total   energy  of   recoil. 
Hence 

PV  '* 
P0)xS=-- (352) 


ARTILLERY   CARRIAGES— THEORY   OF  RECOIL.         455 

In  this  equation,  for  a  given  value  of  S,  everything  is 
known  except  P0,  and  its  value  can  be  determined  so  as  to 
limit  the  recoil  to  a  given  length  5. 

OBJECTIONS. — The  objections  to  friction-brakes  are  : 

1.  They  oppose  to  the  initial  motion  of  the  system,  the 
maximum  resistance,  when  the  velocity  of  recoil  is  greatest, 
and  hence  the  resistance  is  not  uniform  during  the  recoil. 

2.  The  resistance  is  not  constant  for  any  two  consecutive 
shots,  since  it  varies  with  the  condition  of  the  surfaces  in 
contact.     For  the  first  shot,  if  the  surfaces  are  slightly  rusty, 
the  resistance  will  be  great;  for  succeeding  shots,  as  the 
surfaces  become  polished,  the  resistance  decreases,  and  if 
the  surfaces  be  wet  or  lubricated,  the  resistance  decreases. 
All  these  causes  necessitate  a  regulation  of  the  pressure  for 
each  shot. 

3.  The   friction-brake  is  not  automatic,  as  it  has  to  be 
undamped  after  each  shot, to  allow  the  gun  to  run  in  battery, 
and  has  then  to  be  clamped  again  before  firing.     Accidents 
are  liable  to  ocdur  from  this  cause. 

For  these  reasons  the  friction-brake  has  been  abandoned 
for  seacoast  guns,  and  is  only  retained  in  different  forms  in 
field  guns,  where  the  weight  of  the  hydraulic  buffer,  and  its 
liability  to  get  out  of  order,  would  be  objectionable. 

261.  Hydraulic  Brakes — General  Description — Classification — Object 
of  Discussion. 

GENERAL  DESCRIPTION. — This  brake  consists  of  one  or 
more  cylinders  filled  with  non-freezing  liquid,  and  attached 
either  to  the  chassis,  or  to  the  top  carriage.  In  modern 
carriages  the  cylinders  are  generally  two  in  number,  and 
are  attached  to  the  top  carriage  as  near  the  axis  of  the  gun 
as  possible,  to  increase  the  mass  of  the  system  recoiling,  and 
thus  diminish  its  velocity;  and  also  to  bring  the  line  of  re- 
sistance of  the  brakes  as  nearly  as  possible  coincident  with 
the  axis  of  the  bore,  and  thus  diminish  the  overturning 
moment. 

In  each  cylinder  moves  a  piston,  pierced  with  holes 
parallel  to  the  axis  of  the  cylinder,  and  having  a  piston-rod 
attached  to  the  chassis. 


456  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

When  the  piece  and  top  carriage  recoil,  the  cylinders 
move  to  the  rear,  and  the  liquid  is  forced  through  the  holes 
in  the  pistons.  The  resistance  which  the  liquid  opposes  to 
the  motion  of  the  pistons,  limits  the  recoil. 

CLASSIFICATION. — There  are  two  kinds  of  hydraulic 
brakes  in  use : 

1.  Those  with  constant  orifices  and  variable  resistance. 

2.  Those  with  variable  orifices  and  constant  resistance. 
OBJECT  OF  DISCUSSION. — The  principal  points  to  be  de- 
termined in  discussing  a  hydraulic  brake  are : 

1.  The  length  of  recoil ; 

2.  The  area  of  orifice  ; 

3.  The  pressure  in  the  hydraulic  cylinder; 

4.  For  the   hydraulic  brake  of  constant   resistance,  the 
law  of  variation  of  the  areas  of  orifice,  in  order  that  the  re- 
sistance shall  be  constant. 

In  the  discussion,  the  friction  of  the  liquid  is  neglected, 
as  this  is  found  in  practice  to  be  small.  The  flow,  also,  is 
supposed  to  take  place  through  a  thin  partition,  so  that  the 
contraction  of  the  liquid  vein  may  be  neglected. 

The  velocity  at  the  beginning  of  motion,  is  supposed  to 
be  the  maximum  velocity  of  recoil. 

262.  Hydraulic  Brakes  with  Constant  Orifice  and  Variable  Resist- 
ance— Nomenclature  —  Value  of  Total  Resistance  Opposing 
Recoil. 

NOMENCLATURE. — Let  A  be  the  effective  area  of  cross- 
section  of  the  piston  ;  that  is,  the  area  of  the  piston  minus 
that  of  the  piston-rod  and  orifices ; 

a,  the  area  of  the  orifices  of  flow  ; 
*Vm',  the  maximum  velocity  of  recoil  of  the  system ; 
vf,  the  velocity  of  recoil  at  any  time  /; 
v,  the  velocity  of  flow  of    the    liquid  through  the 

orifices  at  that  time  r 
P,  the  weight  of  the  system  recoiling ; 
a,  the  angle   of   inclination   of   the    chassis    to    the 

horizontal ; 

#,  the   density    of    the    liquid    filling    the     cylinder 
(weight  of  unit  volume) : 

*  With  the  brake  acting. 


ARTILLERY   CARRIAGES—  THEORY  OF  RECOIL.         457 

/,  the  coefficient  of  friction  ; 
F,  the  total  resistance  which  opposes  the  recoil. 
VALUE  OF  F.  —  The  total  resistance,  F,  is  composed  of 
two  parts  : 

1.  The  resistance  of  the  brake,  F'. 

2.  The  resistance  due  to  the  friction  of  the  moving  parts, 
and  the  inclination  of  the  chassis,  F". 

We  have  then 

f=F';+-F"  .......    (353) 

The  value  of  F"  is 

F"  =P(sma+fcos<x)  .....     (354) 

The  value  of  F',  the  resistance  of  the  brake,  is  equal  to 
the  total  pressure  exerted  by  the  piston  upon  the  liquid. 

To  determine  this,  we  know  from  the  law  of  continuity 
of  the  fluid,  that  the  volume  of  liquid  displaced  by  the  pis- 
ton, must  be  equal  to  that  which  passes  through  the  orifices 
in  it  ;  hence  we  have 


vat   .....    ...    (355) 

or 


.......  (356) 

This  velocity  v  is  that  due  to  a  height  of  fall 

v  =  tf2gH\    ,  ......    (357) 

and  if  we  suppose  a  column  of  liquid  whose  constant  height 
is  H  and  density  #,  it  will  produce  a  pressure  per  unit  of 
surface  at  its  base,  sufficient  to  cause  the  velocity  of  flow  v. 
Hence  this  is  the  pressure  exerted  per  unit  of  surface  by 
the  piston,  upon  the  liquid,  or  it  is  the  weight  of  a  column 
of  liquid  whose  height  is  H,  density  tf,  and  area  of  base 
unity.  This  pressure  is 

P=8Xffy  .......     (358) 

and  the  total  pressure  on  the  surface  A  of  the  piston  is 

pA  =  F'  =  <*  X  H  X  A,  .....     (359) 


45 8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

whence 

"=-£ (360) 

Substituting  for  v  and  If  in  (357)  their  values  from  (356) 
and  (360),  we  have 


$A 

from  which 


Substituting  the  values  of  F'  and  F"  from  (361)  and  (354) 
in  (353),  we  have  for  the  value  of  the  total  resistance  to 
recoil 

).  •    •    -    (362) 


263.  Length  of  Recoil  with  Constant  Orifice. 

Dividing  both  members  of  equation  (362)  by  M,  we  have 
for  the  acceleration  of  recoil 


Placing 


2/V 
and 

^•(sin  a  +/cos  «)  =  K, 
we  have 


(364) 

M*9 

But 

dx 

»  ^/  » 

and 


•    '     (365) 


ARTILLERY   CARRIAGES—  THEORY  OF  RECOIL.         459 

Whence 

v'dv' 
d*=~  .....    '     (366) 


Integrating  between  the  limits  Vm'  and  v', 
A-'  v'dv'  i  (BVm"  + 

./,     -  BV-  +  K  =*  =  £1^6  log  \^wr+       -  (367) 

Replacing  B  and  K  by  their  values,  we  obtain  an 
equation  giving  the  relation  between  v'  and  x  which  is  too 
complex  for  general  use.  To  simplify  it,  make 

/  =  o,     a  =  o, 

which  is  equivalent  to  supposing  that  the  brake  acts  alone, 
without  friction,  and  that  the  chassis  is  horizontal. 
In  this  case  we  have 

K=o; 
and  substituting  this  value  of  K  in  (367),  we  have 


x  —    »  ,,  , ioff-T- (^68) 

<L43  log  e  v' 

When  v'  —  o,  at  the  end  of  recoil,  x  =  oo  from  equation 
(368),  which  shows  that  the  recoil  will  continue  indefinitely 
if  the  brake  with  constant  orifices  act  without  the  aid  of 
friction. 

264.  Area  of  Orifice  for  a  Given  Length  of  Recoil  with  Constant 
Orifices — Pressure  in  Cylinder. 

Since  for  v'  =  o,  x  =  oo ,  we  cannot  find  directly  from 
equation  (368)  the  area  of  orifice  which  will  limit  the  recoil 
to  a  fixed  length  /.  This  area  can,  however,  for  all  prac- 
tical purposes  be  determined  as  follows: 

Suppose  that  when 


the  remaining  energy  of  the  system  becomes  very  small,  and 
the  carriage  is  about  to  come  to  rest,  and  let  /  denote  the 
length  of  recoil  for  which  v'  =  z//.  Then,  from  (368), 


460  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

(MYloge 

*    =  -  -TF7       .....      (369) 

2/>  log   -=- 

'    ?'/ 

for  the  area  which  will  give  the  length  of  recoil  /. 

PRESSURE   IN   CYLINDER.  —  The   total    pressure    in    the 
cylinder  at  the  beginning  of  recoil  is,  from  (361), 


(370) 


and  at  any  time  at  which  velocity  is  z/  it  is 


and  the  pressure  per  unit  of  area  will  be 
F*       $A*VJ 


2ga* 


and 


(372) 


respectively. 

265.  Hydraulic  Brake  with  Variable  Orifices  and  Constant  Resist- 
ance— Reason  for  Using  it — Objects  of  Discussion — Value  of 
Total  Resistance  opposing  Recoil. 

REASON  FOR  USING  BRAKE  WITH  CONSTANT  RESIST- 
ANCE. — For  the  brake  with  variable  resistance,  equations 
(372)  show  that  the  resistance  is  greatest  when  the  velocity 
of  recoil  is  greatest.  This  is  contrary  to  the  first  condition 
imposed  upon  a  good  brake,  and  it  evidently  throws  a  great 
strain  upon  the  carriage. 

For  this  reason  these  brakes  are  no  longer  used  with 
modern  carriages,  but  are  replaced  by  those  whose  orifice  of 
flow  is  large  at  first,  so  as  to  allow  a  free  flow  of  liquid 
when  the  velocity  of  recoil  is  greatest.  As  the  velocity  of 
recoil  decreases,  and  its  length  increases,  the  orifices  of  flow 
are  gradually  closed  automatically,  and  the  resistance  thus 
made  constant  throughout  the  recoil. 


ARTILLERY   CARRIAG ES— THEORY   OF  RECOIL.         461 

OBJECTS  OF  DISCUSSION. — The  objects  of  the  discussion 
are  to  determine — 

1.  The  length  of  recoil ; 

2.  The  maximum  area  of  the  orifice  of  flow  ; 

3.  The  law   of  variation  of  the  area  of  orifice  in  order 
that  the  resistance  shall  be  constant; 

4.  The  constant  pressure  in  the  cylinder. 

In  this  discussion,  the  first  period  of  recoil,  during  which 
the  resistance  is  approaching  its  constant  value,  is  neglected, 
as  being  very  short,  and  the  resistance  is  supposed  to  be 
constant  from  the  beginning  of  recoil. 

TOTAL  RESISTANCE  OPPOSING  RECOIL. — The  nomen- 
clature being  the  same  as  before,  let  <z0  be  the  maximum 
area  of  orifice  of  flow,  and  suppose  it  to  be  also  the  initial 
area. 

Then  we  have,  as  in  the  case  of  the  brake  with  constant 
orifice,  equation  (354), 

F"  =  P(sm  a  +/COS  a) (373) 

Also,  equation  (361), 

dtfV" 

F'  = r~ (374) 

2ga* 

Since  F1  is  constant  by  hypothesis,  we  must  have  for  any 
other  values  of  vr  and  #,  as  Vmf  and  a0, 


F'  = 
from  which 


F  =  F'  +  F"  =  — — f-  +  P(sin  a  +  f  cos  a).    (3/6) 


266.  Length  of  Recoil  with  Variable  Orifice. 

Dividing  both  members  of  equation  (376)  by  M,  we  have 
for  the  acceleration  of  recoil,  as  before  (equation  363), 

dv'        F  rdA'VJ* 

(377) 


462  TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 

Integrating, 

~  /?  A 3  J7  /a  ~~1 

iin  a  +/COS  a)  \t  +  C.  (378) 


When  /  =  o,  v'  =  FJ  =  C,  hence 

,y^     ~  w  sj  P/y  ^          lo\  '1^  /    \  \O  /  ^// 

Integrating  again, 

V  /a  ~1 

,  .  (380) 


which  is  of  the  same  form  as 

h  =  vt  -  l-gt\ 

and  hence  it  is  the  equation  of  a  uniformly  retarded  motion, 
as  it  should  be,  since  the  resistance  is  constant. 

When   the   recoil   ceases   v   =  o,   and   x  =  /,    the   total 
length  of  recoil,  and  the  corresponding  time  is,  from  (379), 

V  ' 
T=       *  ~'     '     ' 


2paJ   +  ^(sm  a  +  f  cos  or) 

and  this  value  of  T  in  (380)  gives  for  the  total  length  of 
recoil 

i  I  —  V  '*  —  I 

*  =  /=2      <M'Ft"  ' 

2p™>     +  g  (sm  a  +  f  cos  a} 


Equations  (381)  and  (382)  are  similar  to 


v  v* 

t  =  —        h  =  — 

g  tg 


for  bodies  falling  freely  in  vacuo,  under  the  action  of  gravity, 
as  should  be  the  case,  since  we  have  a  constant  force  acting 
in  both  cases. 


ARTILLERY   CARRIAGES—  THEORY   OF  RECOIL.         463 

Placing  equation  (382)  in  the  form 


sn  a 


we  see  that  /  increases  as  Vm'  increases  and  as  a  decreases, 
which  should  be  the  case. 

267.  Maximum  Area  of  Orifice  for  the  Brake  with  Variable  Orifices. 

To  find  the  value  of  a0,  the  maximum  area  of  orifice  in 
this  case,  solve  equation  (382)  for  a*,  and  we  have 

6  /A3  i 


X 


_  _ 
2g-/(sin  a+fcosa)    ' 


for  the  maximum  area  of  orifice. 

Suppose  the  chassis  horizontal  and  the  top  carriage 
mounted  on  rollers  so  as  to  avoid  friction  ;  then 

a  =  o,     /  =  o, 
and  (384)  becomes 

6  1  A* 

*:=-p-  .........  (385) 

The  area  of  orifice  in  this  case  is  independent  of  the 
velocity  of  recoil,  and  hence  we  conclude  that  if  the  top 
carriage  be  placed  on  rollers  and  the  chassis  be  horizontal, 
the  length  of  recoil  will  be  the  same  for  a  given  area  of 
orifice,  no  matter  what  the  initial  velocity  of  the  projectile, 
charge  of  powder,  or  angle  of  fire  may  be. 

268.  Law  of  Variation  of  Areas  of  Orifice  for  Constant  Pressure  in 
Cylinder. 

The  energy  of  the  system  at  the  beginning  of  recoil  is 

PV  " 

;  after  passing  over  the  length  of  recoil  x,  when  the 


£> 

/V 

velocity  is  v't  the  energy  is  -  ,  and  the  work  done  over 

c> 

the  path  x  is  Rx,  in  which 


464  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


-- 

~      dt~g  ~dT' 

From  mechanics,  the  original  energy  of  the  system  is 
equal  to  its  remaining  energy  after  passing  over  a  given 
path,  plus  the  work  done  over  that  path  ;  hence 


or 


(387) 


Since  the  resistance  is  constant  and  the  recoil  uniformly 
retarded,  we  have  from  the  laws  of  constant  forces 


(388) 


Substituting  this  value  of   Fw/a  under  the  radical  sign  in 
(387),  we  have 

_7 (389) 

Since  F'  is  constant,  we  have,  from  (374)  and  (375), 

J2      =  -^-^T-» (390) 

from  which 


Dividing  through  by  Vmf  in  (389)  and  substituting  for 
-j-  its  value  from  (391),  we  have 

-j',-     •     •    •     •     •     (392) 
that  is,  the  areas  vary  as  the  ordinates  of  a  parabola. 


ARTILLERY   CARRIAGES—  THEORY  OF  RECOIL.         465 

These  variable  areas  of  orifice  are  obtained  in  different 
ways,  one  of  the  methods  adopted  in  our  service  being  to 
cut  rectangular  notches  in  the  piston-head,  and  have  bars 
bolted  to  the  sides  of  the  hydraulic  cylinders,  parallel  to  the 
axis,  whose  profile  is  such  that  at  the  origin  the  maximum 
opening  will  be  a0  . 

269.  Profile  of  Rib  for  Constant  Pressure  —  Maximum  Pressure  in 
Cylinder. 

The  profile  of  the  rib  or  throttling-bar  will  then  be  a 
parabola.  As  the  piston  moves  down  the  cylinder,  the 
areas  of  orifice  will  be  gradually  diminished  so  that  the 
pressure  shall  remain  constant. 

The  equation  of  the  parabola  giving  the  profile  of  the 
rib  is  determined  as  follows  : 

Suppose  there  are  n  similar  notches  in  the  piston-head. 

The  area  of  each  one  will  be  -.     Let  b  and  d  be  the  breadth 

n 

and  depth  of  each  notch.      The  rib  in   the  cylinder  must 
have  the  same  breadth,  b,  and  a  variable  depth,  y. 

Then  for  the  area  of  an  orifice  at  any  time  we  have 


=  b(d-  y\  .'.  a  =  nb(d-y\    .    .     .     (393) 
and  this  value  of  a  in  (392)  gives 


for  the  equation  of  the  curve  of  the  profile  of  the  rib. 

PRESSURE  IN   CYLINDER.  —  This   is  given   by  equation 
(375)- 

*          a 

<7=aconstant"    '    '    (395) 


and  per  unit  of  area 

pi       SA*  V  /a 


CHAPTER   VIII. 
POINTING;   PROBABILITY   OF   FIRE. 

POINTING. 
270.  Definitions. 

POINTING. — To  point  a  piece  is  to  give  it  such  a  direction 
and  elevation  that  the  projectile,  when  fired,  will  hit  the 
object  aimed  at. 

OPERATIONS. — The  pointing  of  a  piece  includes  two  dis- 
tinct operations : 

1.  Giving  the  axis  of  the  gun  an  elevation  such  that  the 
projectile  shall  strike  at  the  proper  distance,  or  range,  from 
the  muzzle. 

2.  Giving  the  axis  of  the  gun  such  a  direction  that  the 
projectile  shall  strike  a  given  point  or  object  at  that  distance. 

SIGHTS. — The  instruments  used  in  pointing  are  called 
sights,  and  there  are  two  of  these  for  each  piece :  the  front 
sight  and  the  rear  sight. 

Front  Sight. — This  is  fixed  to  the  muzzle  of  the  gun,  or 
to  one  of  the  rimbases,  usually  the  right,  and  consists  gen- 
erally of  a  fixed  point,  or  thin  edge,  or  of  cross-wires  in  a 
tube,  the  point,  edge,  or  cross-wires  being  at  a  definite  dis- 
tance above  the  axis  of  the  bore,  and  if  on  the  rimbase,  at  a 
fixed  distance  to  the  right  or  left  of  that  axis. 

Rear  Sight. — This  generally  consists  of  a  rod,  bar,  or 
standard,  graduated  in  degrees  or  ranges,  and  fixed  in  a 
socket  on  the  breech  of  the  gun.  This  standard  carries  a 
sliding  notch  or  small  hole,  which  is  capable  of  being  ad- 
justed to  any  height  on  the  rod,  corresponding  to  a  given 
range  or  elevation,  within  service  limits.  The  notch  or  hole 
has  also  a  motion  at  right  angles  to  the  axis  of  the  bore,  to 
correct  for  wind,  drift,  and  other  causes  of  lateral  deflection. 

466 


POINTING— PROBABILITY   OF  FIRE.  467 

In  Fig.  262  let  A  represent  the  front  sight ; 
OC,  the  rear-sight  standard  ; 
EC,  the  sliding  piece,  which  is  supposed  to 

be  at  right  angles  to  OC', 
E,  the  rear-sight  notch. 

Triangle  of  Sight. — Then  the  triangle  OCE  is  called  the 
triangle  of  sight,  and  ECO  is  a  right  angle. 

Zero  of  the  Rear  Sight. — The  point  O,  where  the  line  OA, 
drawn  parallel  to  the  axis  of  the  piece  through  the  top  of 
the  front  sight,  intersects  the  axis  of  the  rear  sight. 

Natural  Line  of  Sight.— The  line  OAB,  parallel  to  the 
axis  of  the  piece,  and  passing  through  the  zero  of  the  rear 
sight  and  the  top  of  the  front  sight. 

Sight  Radius.— The  length  of  the  line  OA. 


D 
•F 


-O 


FIG.  262. 


Artificial  Line  of  Sight. — Any  line,  such  as  EAF,  passing 
through  the  notch  of  the  rear  sight  and  the  top  of  the  front 
sight. 

Natural  and  Artificial  Planes  of  Sight. — The  vertical 
planes  containing  the  natural  and  artificial  lines  of  sight 
respectively. 

Plane  of  the  Rear  Sight. — The  plane  perpendicular  to  the 
axis  of  the  piece,  containing  the  triangle  ECO. 

271.  Cases  which  may  occur  in  Pointing — First  Case — Height  of 
Rear  Sight — Corrections  for  Drift. 

CASES. — The  following  cases  may  occur  in  pointing : 
I.  The  axis  of  the  trunnions  may  be  horizontal,  and  the 

target  situated  in  the  horizontal  plane  passing  through  the 

centre  of  the  muzzle. 


468 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


2.  The  axis  of  the  trunnions  may  be  horizontal,  and  the 
target  situated  above  or  below  the  horizontal  plane  through 
the  muzzle. 

3.  The  axis  of  the  trunnions  may  be  inclined,  and  the 
target  situated  in  the  horizontal  plane. 

4.  The  axis  of  the  trunnions  may  be  inclined,  and  the 
target  situated  above  or  below  the  horizontal  plane. 

The  second  case  is  the  usual  one  for  sea-coast  guns,  and 
the  fourth  for  field  guns. 

FIRST  CASE.— In  Fig.  263  let 
HB   represent   the  line   of   fire   projected   on  the  vertical 

plane  ; 

H'B' ,  the  same  line  projected  on  the  horizontal  plane  ; 
D  and  /?',  the  target ; 

CAD  and  F 'A ' D ',  the  projections  of  the  artificial  line  of 
sight  on  the  vertical  and  horizontal  planes  respect- 
ively. 

Then  CO  is  the  height  of  the  rear  sight  necessary  to  hit 
the  point  D,  and  F'C'  the  correction  for  drift. 


C      A         *, 

t       : 


M 


C'  A' 


FIG.  263. 


If  these  distances  be  known  for  a  given  range  MD,  it  is 
evident  that  by  fixing  the  rear  sight  with  the  proper  eleva- 
tion and  drift,  and  giving  the  axis  of  the  gun  the  direction 
shown,  the  target  will  be  struck. 

To  CALCULATE  HEIGHT  OF  REAR  SIGHT. — In  Fig.  263 
let  h  be  the  height  of  the  rear  sight  CO ; 


POINTING—  PROBABILITY   OF  FIRE.  469 

/,  the  length  of  the  sight  radius  OA  ; 
0,  the  angle  of  elevation  £>MD,the  line  MD  being  hori- 

zontal ; 
6,  the  angle  CA  O  made  by  the  natural  and  artificial 

lines  of  sight  ; 
d,  the  angle  MDG. 
Then  in  the  triangle  MDG  we  have 

MGD  =  BMD  -  MDG. 
But  the  angle  MGD  =  CAO  =  6,  hence 
0  =  0  -  d. 

The  angle  #  is  always  very  small,  being  the  angle  sub- 
tended at  the  target  by  the  vertical  projection  of  the  chase 
of  the  gun  from  front  sight  to  muzzle,  and  hence  we  have 


or 

tan  0  =  tan  0  ; 
but 


hence 

h 

-y  =  tan0;     .-.  h  —  I  tan  0.        .     .     .     (397) 

This  value  of  h  is  laid  off  on  the  rear  sight  from  the  zero, 
and  gives  the  graduation  corresponding  to  the  angle  0. 
CORRECTION  FOR  DRIFT. — In  Fig.  263  let 

D  denote  the  drift  B'D'\ 

d,  the  distance  F' C' ,  or  the  correction  for  drift ; 

#,  the  angle  of  drift,  B'M'D'. 
In  the  similar  triangles  F'A'C  and  N'A'D'  we  have 

FT'       N' D'  N' D' 

£fj>  =  ^-F-t ;     ••-  F'C'  =  J  =  C'A'-^~r     .    (398) 

But 

C'A'  =  CA,  nearly,  =  T^TTT  =  zr"» 

cos  CA  0       cos  0 

or,  since  0  ==  0, 

/ 

~  COS  0° 


47°  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  distance  N' D'  is  very  nearly  equal  to  the  drift  B 'D1 \ 
and  A' N'  =  M' B' ,  or  the  range  R,  very  nearly. 
Making  these  substitutions  in  (398),  we  have 

ID 

d=~R^^> (399) 

272.  Second  Case. 

In  this  case  the  axis  of  the  trunnions  is  horizontal,  and 
the  target  above  or  below  the  horizontal  plane  through  the 
muzzle. 

In  Fig.  264  let  D  be  the  target  situated  above  the  hori- 
zontal plane  MD'r  ; 
0,  the  angle  BMD\ 

a,  the  angle   of   elevation   of  the  target 
above  the  horizontal  plane. 


M^^-^=^^r- 

—. — • — '          1 *  i         . 

D" 

FIG.  264. 

In  the  deduction  of  the  equations  of  Exterior  Ballistics,. 
the  horizontal  plane  MD"  through  the  centre  of  the  muzzle, 
is  alone  considered,  and  all  functions  of  the  trajectory  re- 
ferred to  this  plane. 

By  the  principle  of  the  rigidity  of  the  trajectory,  the 
curve  may  be  revolved  through  a  certain  angle  about  a  hori- 
zontal axis  passing  through  the  point  M,  without  changing 
the  relations  between  the  curve,  its  ordinates  and  angles, 
and  the  chord  MD". 

For  all  practical  purposes  the  points  M  and  A  may  be 
considered  as  coinciding,  and  the  revolution  as  taking  place 
about  the  latter  point. 

Hence  if  the  proper  elevation  OC,  and  correction  for 
drift,  be  obtained  from  equations  (397)  and  (399)  for  the  range 
MD"  —  MD,  on  the  supposition  that  the  target  is  situated 
on  the  horizontal  plane,  and  then  the  gun  be  revolved  about 
the  axis  of  the  trunnions  through  the  angle  a,  till  the  line 


POINTING— PROBABILITY   OF  FIRE. 


471 


0' 


of  sight  CA  passes  through  the  point  Z>,  the  projectile  will 
hit  the.  target,  since  this  is  equivalent  to  revolving  the 
whole  trajectory  for  the  given  range  MD"  through  the  angle 
a.  The  same  discussion  applies  to  the  drift,  which  is  not 
altered  by  the  elevation  of  the  target,  but  is  the  same  for 
the  same  range. 

Hence,  for  this  case,  give  the  rear  sight  the  same  eleva- 
tion and  correction  for  drift  as  if  the  target  were  situated 
on  the  horizontal  plane  through  the  muzzle,  and  then  ele- 
vate the  gun  till  the  artificial  line  of  sight  passes  through 
the  target. 

273.  Third  Case— Errors— Fourth  Case. 

THIRD  CASE. — In  this  case  the  axis  of  the  trunnions  is 
inclined,  and  the  target  is  in  the  horizontal  plane  through 
centre  of  muzzle. 

Let  Fig.  265  be  a  section  of  the  gun  through  the  plane 
of  the  rear  sight,  the  axis  of  the  bore  being  horizontal.  The 
zero  of  the  rear  sight,  and  top 
of  front  sight,  are  projected 
at  O. 

Let  OC  be  the  correct  ele- 
vation, and  FC  the  correction 
for  drift,  which  will  cause  the 
projectile  to  strike  the  target. 

Suppose  that,  due  to  inequal- 
ities of  the  ground  or  other 
causes,  the  gun  is  rotated  to  the 
right,  about  the  axis  of  the  bore, 
through  the  angle  (9.  The  zero 
of  the  rear  sight,  and  top  of 
front  sight,  will  now  be  pro- 
jected at  O',  and  the  new  posi- 
tion of  the  rear  sight  will  be 
O'C'F'.  The  axis  of  the  bore 
or  line  of  fire  has  not  changed 
its  position,  and  the  gun,  if 
fired,  will  hit  the  target.  But 
if  the  gun  be  resighted  before 
firing,  using  the  sights  in  their  FIG.  265. 


472  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

revolved  position,  the  artificial  line  of  sight  will  no  longer 
pass  through  the  target,  and  if  it  be  made  to  do  so, , this  will 
change  the  position  of  the  line  of  fire,  or  axis  of  bore,  and 
the  projectile  will  no  longer  strike  the  target. 

ERRORS. — By  this  rotation  of  the  gun,  the  following 
errors  have  been  introduced  : 

i.  Instead  of  having  the  proper  vertical  height  of  rear 
sight  equal  to  OC  or  O"C",  it  is  equal  to  0"C"'t  or  too 
small. 

This  may  be  explained  as  follows :  The  front  sight,  and 
zero  of  rear  sight  projected  at  <9,  have  been  lowered  verti- 
cally by  the  rotation  a  distance  O"O ;  and  since  the  height  of 
rear  sight  above  the  zero  should  remain  unchanged,  this 
height  should  now  be  O"C" ,  equal  to  OC.  But  the  rear- 
sight  notch  is  actually  at  a  height  O'fC'",  and  hence  is  too 
low  by  the  distance  C"C'". 

2.  Instead  of  having  the  proper  correction  for  drift  FC, 
we  have  F[VC',  which  is  too  small. 

3.  The   artificial   line   of   sight,  before   rotation    occurs, 
passes  through  the  point  F,  and  the  top  of  the  front  sight 
projected  at  O.     Hence,  looking  from  the  rear,  the  line  of 
sight  FO  is  oblique  to  the  axis  of  the  gun  and  diverges  to 
the  right. 

After  rotation  the  artificial  line  of  sight  passes  through 
F',  and  the  top  of  the  front  sight  projected  at  O'.  Hence, 
looking  from  the  rear,  this  new  line  of  sight  F'O'  is  oblique 
to  the  axis  of  the  gun  and  diverges  to  the  left.  If,  therefore 
the  gun  were  correctly  pointed  before  rotation,  and  be  re- 
pointed  after  rotation,  the  projectile  will  deviate  to  the 
right. 

This  latter  error  is  shown  in  plan,  the  same  letters  being 
used.  It  is  of  very  frequent  occurrence  in  small-arms  firing, 
when  the  rear  sight  is  not  held  vertically,  the  bullet  deviat- 
ing to  the  side  toward  which  the  sight  is  inclined. 

To  avoid  these  errors  it  is  necessary  to  construct  the 
rear  sight  so  that  its  standard  or  upright  will  rotate  about 
the  point  O.  By  means  of  a  spirit-level  fixed  at  right  angles 
to  the  axis  OC,  this  axis  can  always  be  kept  in  a  vertical 
plane.  With  this  arrangement,  whenever  the  front  sight 


POINTING— PROBABILITY   OF  FIRE.  473 

and  the  zero  of  the  rear  sight  are  lowered  vertically  through 
a  distance  O"O,  by  rotation  due  to  the  inequality  of  the 
ground  or  other  causes,  the  notch  of  the  rear  sight  will  be 
lowered  the  same  amount,  the  vertical  heights  OC  and  O'C" 
and  the  correction  for  drift  remaining  unchanged.  This 
arrangement  is  made  in  all  field-gun  sights. 

With  this  arrangement  of  the  sights  the  pieces  are  pointed 
as  in  the  first  case. 

FOURTH  CASE. — In  this  case  the  axis  of  the  trunnions 
is  inclined,  and  the  target  above  or  below  the  horizontal 
plane. 

If  the  standard  of  the  rear  sight  rotates  about  the  zero, 
as  explained,  the  pointing  is  executed  as  in  case  two. 


FIG.  266. 

274.  Permanent  Angle  of  Drift. 

Referring  to  Fig.  263,  it  is  evident  that  the  drift  increases 
more  rapidly  than  the  range,  and  hence  each  range  requires 
a  special  correction  for  drift.  It  is  found,  however,  that 
within  certain  limits  of  error,  a  permanent  correction  may 
be  made  for  drift,  by  giving  the  rear-sight  standard  an  in- 
clination to  the  left  at  a  certain  angle  i  with  the  vertical. 
This  applies  only  to  small  arms  where  the  barrel  can  be 
held  with  the  front  sight  vertical,  and  to  guns  with  fixed 
platforms,  where  the  axes  of  the  trunnions  are  horizontal. 
For  field-guns,  as  before  explained,  the  standard  of  the  rear 
sight  is  kept  vertical. 

To  determine  this  permanent  angle,  in  Fig.  266 

let  i  =  the  angle  FOC  required  ; 
h  =  OC,  the  height  of  rear  sight ; 
d  —  FC,  the  correction  for  drift , 
1=  OA,  the  length  of  the  sight  radius; 


474  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

0  =  the  angle  of  elevation  BAD  ; 
e  —  the  angle  DAD'. 

Then  in  the  triangle  FOC  we  have 

d  =  h  tan  i  ; 
but  from  (397), 

h  =  /tan  0  ; 

hence 

d  =  I  tan  0  tan  i, 

tan  i  —  -7——  —  .......     (400) 

/  tan  0 

From  the  triangle  OA  C  we  have 

AC=tsec0,     ......    (401) 

and  from  FAC, 

d  —  AC  tan  e, 
or  from  (401), 

d  —  I  sec  0  tan  *;.,,.  (4010) 
but  from  the  figure, 

drift 


tan  e  =  -^-^  = 

AD       range 

hence  in  (4010) 

d  =  /sec  0-77,     .....     (402) 

Z>  denoting  the  drift  and  ^  the  range. 

Substituting  this  value  of  d  in  (400),  we  have 


It  is  known  from  Exterior  Ballistics  that  sin  0  increases 
more  rapidly  than  the  range,  and  so  also  does  D.  Hence 
these  variations  partly  correct  each  other  and  tend  to  make 
the  angle  i  constant,  and  hence  this  constant  correction  for 
drift  can  be  applied  without  great  error.  For  long  ranges, 
however,  this  correction  is  only  partial,  and  an  additional 
one  must  be  made  with  the  sight. 


POINTING— PROBABILITY  OF  FIRE.  4/5 

From  equation  (403)  the  amount  of  drift  corrected  for  by 

this  method  is 

D  —  R  sin  0  tan  i ; 

if  any  greater  drift  exists,  as  D',  the  difference, 

Df  —  D  =  D'  —  R  sin  0  tan  i, 

\ 
must  be  corrected  for  by  the  sight. 

275.  Indirect  Pointing. 

When  the  target  cannot  be  seen  from  the  gun,  the  above 
methods  must  be  modified. 

The  simplest  case  is  that  of  mortar -firing,  where  the  tar- 
get is  invisible  from  the  piece,  but  may  be  seen  from  the 
parapet  of  the  emplacement.  In  this  case  the  plane  of  sight 
is  established  by  plummets  suspended  from  trestles,  the  ele- 
vation given  approximately,  and  the  mortar  moved  or  trav- 
ersed, till  the  planes  of  fire  and  of  sight  coincide. 

The  second  case  is  where  the  target  cannot  be  seen  from 
the  battery,  but  is  visible  from  some  place  sufficiently  near 
to  communicate  with  the  battery.  In  this  case  an  observer 
watches  the  point  of  fall,  and  signals  to  the  battery  its  posi- 
tion as  to  range  and  deviation.  The  aim  is  then  corrected, 
and  this  is  continued  till  the  target  is  struck.  An  auxiliary 
mark,  which  is  visible  from  the  gun,  is  selected,  and  the  sights 
directed  upon  this  mark  before  each  shot.  When  the  target 
is  struck,  the  piece  is  thereafter  sighted  upon  this  auxiliary 
mark,  without  changing  the  sights  as  adjusted  for  that  shot. 
If  a  suitable  mark  cannot  be  obtained,  the  bearing  of  the 
target  may  be  observed  by  a  compass.  Then  by  placing 
the  compass  in  rear  of  the  gun,  the  bearing  of  the  target  may 
be  laid  off  by  stakes  and  the  gun  directed  upon  them,  the 
firing  being  corrected  by  an  observer. 

In  some  services  sights  are  arranged  so  that  they  may 
be  reversed  in  position ;  that  is,  the  rear  sight  is  placed  in 
the  position  ordinarily  occupied  by  the  front  sight,  and  the 
latter  replaces  the  rear  sight.  (See  /-inch  howitzer  sight, 
page  493.)  In  this  case  the  marking  stake  or  stakes  are 
placed  in  rear,  and  the  sights  directed  upon  them.  Reflect- 
ing sights  are  also  used  when  cover  is  of  importance,  and 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 

for  turrets,  the  sights  are  placed  on  the  exterior,  and  at  the 
opposite  extremity  of  the  diameter  upon  which  the  gun  is 
situated.  While  the  turret  is  revolved  180°  for  loading,  the 
sighting  is  effected,  and  when  the  gun  is  loaded,  a  traverse 
of  1 80°  brings  the  gun  into  firing  position. 

276.  Causes  of  Deviations  in  Pointing — Effect  of  Wind. 

CAUSES  OF  DEVIATIONS. — When  a  gun  is  correctly 
pointed,  as  explained,  the  projectile  should  pass  through 
the  target.  This,  however,  does  not  occur  unless  further 
corrections  be  made  to  eliminate  other  causes  of  error. 

The  principal  of  these  are : 

1.  The  effect  of  the  wind. 

2.  Errors  in  estimating  distance  to  target. 

3.  Effects  of  light  on  sights. 

4.  Personal  errors  of  the  eye. 

5.  Errors  in  height  of  front  and  rear  sights. 

6.  Motion  of  target. 

7.  Rotation  of  the  earth. 

8.  Variations  in  ammunition. 

9.  Jump. 

EFFECT  OF  WIND. — The  effect  of  wind  is  to  increase  or 
decrease  the  range,  according  as  it  is  blowing  from  rear  to 
front,  or  from  front  to  rear,  and  to  increase  or  decrease  the 
drift  of  the  projectile. 

The  velocity  of  the  wind  is  generally  expressed  in  miles 
per  hour,  and  is  obtained  from  an  anemometer.  A  vane  or 
other  indicator  gives  its  direction.  Let  W  be  the  velocity 
of  the  wind  in  miles  per  hour,  and  <p  the  angle  which  its 
direction  makes  with  the  line  of  fire.  The  angle  0  is  meas- 
ured from  front  to  rear,  being  zero  when  the  wind  blows 
directly  from  the  front  along  the  line  of  fire. 

Then  the  component  which  increases  or  decreases  the 
range  is  W  cos  0,  and  that  which  increases  or  decreases 
the  drift  is  W  sin  0. 

The  effect  upon  the  increase  or  decrease  of  range  is  ob- 
tained by  reducing  W  to  feet,  and  regarding  the  projectile 
as  having  a  velocity  equal  to  v  +  W  cos  0  or  v  —  W  cos  0. 


POINTING— PROBABILITY   OF  FIRE. 

Using  these  values  for  v  in  the  ballistic  formulas,  the  effect 
of  the  wind  along  the  range  can  be  calculated. 

The  component  which  produces  deviation  is  W  sin  0. 
Various  formulas  are  given  for  calculating  its  effect,  but  the 
subject  is  very  difficult. 

When  the  wind  is  blowing  from  the  left,  its  relative  mo- 
tion with  respect  to  the  projectile  is  less  because  the  latter 
is  moving  in  the  same  direction.  When  it  blows  from  the 
opposite  direction  the  reverse  is  the  case.  To  correct  for 
lateral  deviation  due  to  wind,  the  drift-slide  is  set  towards 
the  wind.  That  is,  if  the  wind  is  from  the  left,  the  slide  is 
moved  to  the  left. 

For  small-arm  firing,  the  direction  of  the  wind  is  ex- 
pressed by  a  clock-face  notation,  the  clock  being  supposed 
to  be  held  in  the  hand  of  the  firer,  with  the  Xll-o'clock 
mark  toward  the  target  and  the  Ill-o'clock  mark  to  the 
right.  A  wind  blowing  directly  from  the  target  is  called  a 
Xll-o'clock  wind  ;  one  directly  from  the  left,  a  IX-o'clock 
wind,  etc. 

Assuming  the  force  of  the  wind  as  unity,  a  table  is  given 
in  the  "Rifle  and  Carbine  Firing,"  showing  the  proportions 
of  the  rectangular  components  of  the  different  winds,  and  it 
is  found  practically,  that  the  lateral  deflections  produced  by 
them  are  proportional  to  these  components. 

The  amount  of  lateral  deviation  produced  by  a  wind 
blowing  at  right  angles  to  the  line  of  fire,  with  a  velocity  of 
one  mile  per  hour,  is  called  the  coefficient  of  deviation. 
Calling  this  coefficient  k,  we  have  for  any  wind  whose 
velocity  is  W,  and  which  makes  an  angle  0  with  the  line  of 
fire,  for  any  given  range, 

D  —  kWsiu  0. 

The  relation  between  k  and  R  must  be  determined  by 
experiment. 

277.  Estimating  Distances — By  the  Eye — By  Sound — Le  Boulenge" 
Telemeter. 

It  is  evident  that  unless  the  distance  of  the  target  be 
known,  the  proper  elevation  and  correction  for  drift  cannot 


478  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

be  given,  since  these  depend  on  the  range.  In  actual  opera- 
tions the  distance  of  the  target  is  seldom  known.  For  sea- 
coast  guns,  the  channel  or  harbor  is  surveyed  and  plotted, 
and  buoys  may  be  planted  at  different  known  distances.  In 
siege  operations,  the  distance  of  the  target  may  be  obtained 
by  observations  with  various  instruments  of  precision ;  but 
for  field  artillery,  where  time  is  lacking,  the  distance  must 
be  obtained  rapidly  by  estimation,  by  range-finders,  or  by 
trial  shots. 

Distances  may  be  estimated — 

1.  By  the  eye  ; 

2.  By  sound. 

BY  THE  EYE. — This  method  requires  considerable  prac- 
tice to  obtain  results  of  any  accuracy.  For  short  ranges 
the  eye  may  be  trained  by  trial,  by  observing  carefully 
the  appearance  presented  by  known  objects  at  different  dis- 
tances, such  as  the  height  of  a  man,  the  parts  of  his  dress, 
etc.,  which  are  visible  at  those  distances.  Each  individual 
must  form  a  standard  of  comparison  for  himself;  and  since 
this  method  is  only  applicable  for  relatively  short  distances, 
it  is  of  more  importance  for  small-arm  fire. 

Objects  vary  in  appearance  according  to  the  nature  of 
the  ground,  being  apparently  nearer  for  level  ground  ;  also 
on  a  clear  day,  or  with  a  distinct  background,  they  appear 
nearer  than  under  opposite  conditions. 

BY  SOUND. — This  method  is  based  on  the  fact  that 
sound  travels  about  i  TOO  feet  per  second  in  air.  Hence,  if 
the  time  in  seconds  be  noted  between  the  flash  and  the  re- 
port of  a  gun,  or  between  the  flash  and  the  report  of  a  shell 
fired  from  the  battery,  the  distance  is  obtained  by  multiply- 
ing the  time  in  seconds  by  noo  feet.  This  time  may  be 
measured  by  a  stop-watch,  or  by  counting  the  number  of 
steps  taken  in  the  interval,  and  knowing  the  number  of 
similar  steps  which  the  observer  takes  per  second. 

LE  BOULENGE  TELEMETER. — An  instrument  called  the 
Le  Boulenge  telemeter  is  used  for  measuring  distances  by 
sound.  It  consists  of  a  glass  tube  filled  with  liquid,  in 
which  a  disk  is  placed,  whose  specific  gravity  is  slightly 
greater  than  that  of  the  liquid.  When  the  tube  is  held  ver- 


POINTING—  PROBABILITY   OF  FIRE. 


479 


tical,  the  disk  falls  through  the  liquid  with  a  motion  which 
is  nearly  uniform.  To  use  the  telemeter,  the  tube  is  held 
horizontal,  with  the  disk  at  zero.  When  the  flash  is  seen,  it 
is  turned  quickly  to  a  vertical  position  ;  when  the  report  is 
heard,  it  is  turned  back  to  a  horizontal  position.  A  scale  on 
the  tube  gives  the  range  directly,  corresponding  to  the  dis- 
tance passed  over  by  the  disk. 

It  is  evident  that  it  would  be  difficult  in  practice  to 
observe  the  burst,  and  hear  the  report  of  any  particular 
shell. 

278.  Range-Finders  —  Principle  —  Class  1. 

The  estimation  of  distances  by  the  eye  and  by  sound 
being  so  inaccurate,  instruments  called  range-finders  or 
telemeters  have  been  devised  to  measure  the  distance  to  the 
target. 


FIG.  267. 


PRINCIPLE.— In  Fig.  267  let  C  be  the  target. 

In  the  isosceles  triangle  ADC,  if  the  angles  at  A  and  D, 
and  the  base  AD,  are  known,  the  angle  ACD  can  be  found, 
arftl  we  have 

BC  = 


tan  ±  A  CD' 


or  in  the  right-angled  triangle  ABC  or  BCD,  if  the  angle 
.at  A  or  D  be  known,  we  have 


BC= 


4^0  TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 

or 

AB 

AC  = 


sin  ACS' 

The  object  of  these  instruments  is  to  measure  rapidly 
and  accurately  the  angles  A  and  D. 

To  avoid  calculations,  the  angles  A  and  D  are  so  chosen 
that  the  value  of  the  tangent  or  sine  of  C  shall  be  some  sim- 
ple number,  as  j1-^,  J^-,  ^,  etc. ;  or  the  angles  may  vary  and 
the  base  have  a  fixed  value,  the  corresponding  multipliers 
being  inscribed  on  the  instrument. 

This  divides  the  instruments  into  two  general  classes — 

1.  Those  having  fixed  angles  and  variable  bases  ; 

2.  Those  having  variable  angles  and  fixed  bases 


FIG.  268. 

and  a  third  class  which  combines  the  qualities  of  the  two 
above,  viz., 

3.  Those  having  variable  angles  and  variable  bases. 

CLASS  i. — In  this  class  of  range-finders  the  base  is  pro- 
portional to  the  range.  This  gives  greater  accuracy,  as 
with  a  small  base,  a  slight  error  in  measurement  of  either 
angles  or  base  leads  to  a  large  error  in  range.  The  general 
idea  of  this  class  of  instruments  is  as  follows  :  Two  mirrors 
are  fixed  at  an  angle,  say,  of  44°  if  (Fig.  268).  A  ray  of 
light  striking  one  of  these  mirrors  is  reflected  twice,  and 
according  to  a  well-known  principle  of  optics,  the  ray,  after 
two  reflections,  makes  with  the  original  direction  of  the  inci- 


POINTING—  PROBABILITY  OF  FIRE.  481 

dent  ray,  an  angle  of  88°  34',  or  twice  the  angle  of  the 
mirrors.  An  observer  standing  at  A  and  looking  toward  />, 
sees  /?  directly,  and  by  reflection  in  the  mirrors,  makes  the 
image  of  C  coincide  with  B.  The  point  A  is  then  marked 
by  a  stake.  Moving  to  B,  which  must  be  found  by  moving 
along  AB  and  looking  towards  A,  the  reflection  of  C  is 
made  to  coincide  with  A.  The  angle  at  C  is  then 

1  80°  -2  X88°  34'  =  2°  52',    . 
and  measuring  AB  we  have 


_ 

SSlFSff     7T 

=  40  X  \AB  =  2oAB. 


FIG.  269. 

279.  Range-finders— Class  2— Class    3— Depression    Range-finders 
— Range  and  Position  Finder. 

CLASS  2. — In  this  class  we  have  a  fixed  base  and  a  variable 
angle.  To  save  time,  the  instruments  are  generally  adjusted 
so  that  the  range  can  be  read  off  at  once.  As  the  measure- 
ments must  be  very  accurate,  telescopes  are  often  used  to 
measure  the  angles,  and  this  necessitates  a  very  accurate 
mounting  and  increases  the  difficulty  of  transportation. 

CLASS  3. — These  instruments  can  be  used  by  either 
method,  but  the  variable  base  is  generally  preferred. 

DEPRESSION  RANGE-FINDERS.— Let  AB,  Fig.  269,  repre- 
sent the  vertical  height  of  a  gun,  or  of  a  range-finder,  above 
the  surface  of  the  water,  and  C  an  object,  such  as  a  ship, 
whose  distance  is  to  be  determined.  If  the  angle  C'BC  be 
-measured,  and  the  height  AB  be  known,  it  is  evident  that 
the  distance  BC  can  be  determined  as  before.  These  instru- 


482 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


ments  are  called  depression  range-finders,  the  angle  being 
measured  in  a  vertical  plane. 

RANGE  AND  POSITION  FINDERS. — In  sea-coast  batteries 
it  is  often  necessary  to  fire  at  objects,  such  as  ships,  which 
cannot  be  seen  from  the  guns.  In  this  case  it  is  necessary 
to  find  not  only  the  range  but  also  the  position  of  the  object, 
which  is  generally  in  motion,  in  order  to  hit  it  at  any  given 
time.  An  instrument  used  lor  this  purpose  is  the  Fiske 
Range  and  Position  Finder,  invented  by  Lieut.  Fiske  of  the 
U.  S.  Navy. 


FIG.  270. 


FIG.  271. 


280.  The  Fiske  Range-finder. 

In  Fig.  270  let  A  represent  the  target,  and  BC  a  known 
base.     Then 

AC:  BC::  sin  ABC  :  sin  BAC. 


sin  BAC 

The  angle  ABC  can  be  readily  measured.  The  angle 
BAC=-  DBE,  the  line  BE  being  parallel  to  AC.  The  Fiske 
Range-finder  measures  the  angle  DBE  by  the  use  of  the 
Wheatstone  bridge,  as  follows  : 

Suppose  the  two  semicircles  in  Fig.  270  replaced  by  two 
metallic  arcs  (Fig.  271).  At  the  centre  of  each  of  these  arcs 


POINTING— PROBABILITY  OF  FIRE.  483 

is  pivoted  a  telescope,  the  pivot  of  which  is  connected  to  a 
battery,  B.  The  telescopes  are  in  electrical  contact  with 
the  arcs.  These  metallic  arcs  are  connected  at  their  ex- 
tremities with  a  galvanometer,  c,  the  whole  forming  a 
Wheatstone  bridge,  whose  arms  are  aabb. 

When  the  two  telescopes  are  pointed  on  the  object  A, 
it  is  evident  that  the  arms  of  the  bridge  are  unequal,  and 
hence  do  not  balance,  and  this  fact  is  indicated  by  the  de- 
flection of  the  needle  of  the  galvanometer.  The  arc  FD  is 
noted. 

By  swinging  the  telescope  at  F,  around,  till  the  needle  of 
the  galvanometer  indicates  zero,  the  bridge  balances,  the  tele- 
scope being  parallel  to  the  one  at  C,  and  the  arc  or  angle 
DF  —  FE  —  DE  is  equal  to  the  angle  at  A.  From  this  the 
distance  AC  can  be  calculated,  or  be  read  off  directly  on  a 
properly  constructed  scale. 

Generally,  in  using  the  instrument,  the  telescopes  are 
mounted  at  a  distance  from  the  battery  where  the  view  is 
uninterrupted,  while  the  galvanometer  is  at  the  gun.  The 
observers  keep  the  telescopes  constantly  directed  on  the 
target,  and  the  man  at  the  gun  balances  the  bridge,  by  intro- 
ducing a  variable  resistance  into  the  circuit,  till  the  needle 
stands  at  zero.  This  variable  resistance  is  graduated  so  as 
to  indicate  the  range  corresponding  to  the  resistance  in- 
troduced. 

281.  The  Fiske  Position-finder— Range  by  Trial  Shots. 

To  find  the  position  of  the  object,  the  Fiske  Range- 
finder  is  modified  as  follows,  Fig.  272. 

Let  A  and  B  be  the  arcs  with  their  telescopes  as  de- 
scribed, and  D  a  chart  drawn  to  scale,  on  which  are  two 
metallic  arcs,  A'  and  B' .  The  arc  A'  is  connected  electri- 
cally with  A  and  with  a  galvanometer,  A",  forming  a 
Wheatstone  bridge,  and  in  the  same  way  the  arc  B'  is  con- 
nected with  B,  and  with  the  galvanometer,  B".  The  arc  A' 
carries  a  metallic  rule,  AC',  pivoted  at  the  centre  of  the  arc, 
and  B1  a  rule,  B'C',  similarly  pivoted. 

When  the  rule  AC  is  parallel  to  the  telescope  at  A,  the 
galvanometer  A"  is  at  zero.  When  B'C'  is  parallel  to  the 


484 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


telescope  at  B,  the  galvanometer  B"  is  at  zero.  Hence  their 
intersection  C'  marks  the  position  of  the  object  on  the  chart. 
Let  G  be  the  gun  in  battery,  and  Gf  its  corresponding  posi- 
tion on  the  chart.  The  gun  has  a  metallic  arc  with  which  a 
pointer  is  in  contact,  and  the  arc  G'  has  a  metallic  rule,  G 'C ', 
in  contact  with  it.  The  gun  G  with  its  arc  and  pointer,  and 
the  metallic  rule  G ' C ',  are  electrically  connected  with  a  gal- 
vanometer, G",  near  the  gun,  forming  a  third  Wheatstone 
bridge.  It  is  evident  that  by  traversing  the  gun  in  azimuth 
till  its  axis  is  parallel  to  the  rule  G'C,  the  galvanometer  G" 


FIG.  272. 

will  indicate  zero,  and  the  gun  will  have  the  proper  direc- 
tion. The  elevation  may  be  telephoned  from  the  observing 
station,  or  else  the  gunner,  knowing  the  range  and  direction 
of  the  object,  may  take  the  elevation  directly  from  a  range 
table.  Other  arrangements  of  the  same  nature  may  be 
made  with  this  instrument,  using  the  principle  of  the 
Wheatstone  bridge. 

RANGE   BY  TRIAL  SHOTS.  —  Owing  to   various  causes, 


POINTING— PROBABILITY   OF  FIRE.  485 

the  determination  of  distances  in  the  field  by  range- 
finders  is  attended  with  difficulty,  and  the  method  actually 
adopted  in  all  services  is  that  by  trial  shots.  Two  plans  are 
used. 

In  the  first  a  percussion-shell  is  fired  with  an  elevation 
which  will  cause  it  to  strike  short  of  the  target.  The  point 
of  fall  is  observed.  A  second  shell  is  then  fired  with  an 
elevation  which  will  cause  it  to  strike  beyond  the  target. 
Its  point  of  fall  is  also  observed.  The  target  is  then  en- 
closed in  a  fork. 

Taking  a  mean  of  these  two  elevations  will  give  a  still 
closer  approximation.  If  this  shot  falls  short,  a  mean  of 
this  elevation  and  of  that  beyond  will  give  another  approx- 
imation, and  so  on.  ' 

By  this  means  the  range  is  soon  found. 

The  second  method  is  to  fire  the  first  shot  short,  and 
then  increase  the  elevation  slightly,  and  so  on  by  succes- 
sive increments  till  the  proper  range  is  attained.  The  diffi- 
culty is  in  observing  accurately  the  point  of  fall  for  long 
ranges. 

282.  Effect  of  Light— Errors  of  the  Eye — Errors  in  Height  of  Front 
and  Rear  Sights. 

ERRORS  DUE  TO  LIGHT. — In  clear  weather  shots  usually 
fall  short,  since,  in  a  bright  light,  objects  appear  nearer,  and 
the  distance  is  underestimated,  and,  in  addition,  a  finer  sight 
is  taken,  owing  to  the  distinctness  of  the  front  sight.  The 
converse  is  true  on  a  dark  day.  With  regard  to  lateral 
deviation,  if  one  side  of  the  sight  is  brighter  than  the  other 
the  deviation  will  be  from  the  light. 

ERRORS  OF  THE  EYE. — These  vary  with  different  indi- 
viduals, and  must  be  corrected  by  training. 

ERRORS  IN  HEIGHT  OF  FRONT  AND  REAR  SIGHTS. — In 
the  previous  discussions  it  has  been  assumed  that  the  zero 
of  the  rear  sight,  and  the  top  of  the  front  sight,  are  at  the 
same  distance  from  the  axis  of  the  piece.  If  this  be  so,  the 
natural  line  of  sight  is  parallel  to  the  axis  of  the  piece  in  all 
positions,  and  hence  the  vertical  plane  containing  this  line 
is  likewise  parallel  to  the  plane  of  fire  in  all  positions. 


486 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


A-~~ 


If,  however,  the  height  of  the  front  sight  is  not  the  same 
as  that  of  the  zero  of  the  rear  sight,  an  error  is  introduced* 
To  show  this,  in  Fig.  273  let  A  and  B 
be  the  vertical  projections  of  the  rear 
and  front  sights,  respectively,  and  AB 
the  horizontal  projection  of  the  natu- 
ral line  of  sight  when  the  axis  of  the 
trunnions  is  horizontal. 

Suppose  that,  due  to  inequalities  of 
the  ground,  the  axis  of  the  trunnion  is 
revolved  through  the  angle  0. 

Then  A'  and  B'  will  be  the  verti- 
cal projections  of  the  rear  and  front 
sights,  and  A' B'  the  horizontal  projec- 
tion of  the  natural  line  of  sight.  This 
line  is  now  inclined,  in  its  revolved 
position,  to  the  axis  of  the  piece,  and 
hence  in  the  revolved  position  the 
plane  of  sight  will  intersect  *he  plane 
of  fire.  Hence,  to  an  observer  behind  the  gun,  if  the  line  of 
sight  be  directed  on  the  target  T,  the  gun  will  shoot  to  the 
left. 

This  error  is  similar  to  that  discussed  in  subject  273.  In 
that  case  it  can  be  removed  by  keeping  the  rear  sight  verti- 
cal. The  error  in  the  present  case  can  only  be  removed  by 
making  the  heights  of  front  sight  and  of  zero  of  rear  sight 
equal. 

283.  Motion  of  Target  —  Rotation  of  the  Earth  —  Variations  in 
Ammunition. 

The  target  may  move  directly  toward  or  from  the  gun, 
at  right  angles  to  the  line  of  fire,  or  oblique  to  that  line.  As 
the  last  case  includes  both  the  others,  it  will  be  considered. 

Let  AB,  Fig.  274,  be  the  line  of  fire,  and  BC  the  direction 
of  motion  of  the  target,  making  the  angle  0  with  the  line  of 
fire.  Suppose  the  range  AB  and  the  rate  of  motion  of  the 
object  known. 


POINTING— PROBABILITY  OF  FIRE.  487 

During  the  time  that  the  projectile  is  moving  over  the 
distance  AB  the  object  has  moved  over  the  distance  BC. 
Let  v  denote  the  velocity  of  the  object  and  t  the  time  of 
flight  of  the  projectile  ;  then 

BC  =  vt. 

Suppose  the  correction  for  drift  to  be  such  as  to  cause 
the  projectile  to  strike  at  B.  Then  to  hit  the  object  the 
correction  should  be  made  to  cover  the  additional  distance, 

D  +  CC  =  D  +  vt  sin  0, 

in  a  direction  toward  the  motion  of  the  target.     If   this 
motion  is  not  known  it  must  be  estimated. 

This  will  still  leave  a  small  error  in  range  BC'  =  vt  cos  0 
which  must  be  compensated  for  by  a  slight  increase  in  ele- 


B    C' 

FIG.  274. 


vation,  or  by  retaining  the  elevation  corresponding  to  AB 
and  aiming  beyond  the  target  the  estimated  distance  BC'. 

ROTATION  OF  THE  EARTH. — This  is  not  generally  taken 
into  account.  Its  effect  in  the  northern  hemisphere  is  to 
cause  projectiles  to  deviate  to  the  right. 

VARIATIONS  IN  AMMUNITION. — The  effect  of  increasing 
the  charge  and  density  of  loading  is  to  increase  the  initial 
velocity.  That  of  increasing  the  weight  of  the  projectile  is 
to  decrease  this  velocity,  as  has  already  been  shown  in  Inte- 
rior Ballistics.  With  modern  guns  these  variations  in 
ammunition  are  very  slight,  and  their  effects  may  be  neg- 
lected. Variations  in  moisture  also  affect  the  initial  velocity, 


488  TEXT- BOOK  OF  ORDNANCE  AND    GUNNERY. 

a  damp   powder  giving   less  velocity  and    a   dry  powder 
greater  velocity,  for  the  reasons  previously  explained. 

Also  the  heating  of  the  bore  increases  this  initial  velocity, 
since  less  heat  is  lost  by  the  gases. 

284.  Jump. 

This  error  is  caused  by  the  motion  of  the  gun  upon 
discharge,  due  to  the  elasticity  of  tke  parts  of  the  carriage, 
the  lack  of  accurate  fitting  of  gun  to  carriage,  the  vibration 
of  the  chase,  etc.  It  varies  with  different  guns  and  car- 
riages, and  is  determined  by  experiment  for  any  particular 
gun  as  follows: 

In  Fig.  275  let  AB  be  a  vertical  screen  or  target,  placed 


FIG.  275. 

at  such  a  distance  from  the  muzzle  of  the  gun  O  that  it  will 
not  be  affected  by  the  blast.  Let  OB  be  the  axis  of  the  bore, 
supposed  horizontal.  The  point  B  where  the  axis  of  the 
bore  prolonged  pierces  the  target  is  found  by  inserting  a 
disk  in  the  breech  of  the  gun  with  a  small  peep-hole  in  the 
centre,  and  placing  in  the  muzzle  a  pair  of  cross-hairs  whose 
intersection  is  at  the  axis  of  the  bore.  Looking  through 
the  peep-hole  and  at  the  cross-hairs,  the  point  B  is  marked 
on  the  target.  When  the  gun  is  fired,  suppose  OA  to  be  the 
line  of  departure.  Then  AOB  is  the  angle  of  jump  required. 
The  projectile  will  strike  the  target  at  some  point  C.  From 
the  triangle  AOB  we  have 

AB      AC+CB 


tan  AOB  = 


OB~          OB 


POINTING—  PROBABILITY   OF  FIRE.  489 

From  the  laws  of  falling  bodies  we  have 

(403*) 


For  the  short  distance  OB  we  may  regard  the  velocity 
of  the  projectile  as  uniform.  Denoting  this  velocity  by  vt 
and  the  distance  OB  by  a,  we  have 


This  value  of  /  in  (4030)  gives 


The  distance  BC  to  the  centre  of  shot-hole  C  can  be 
measured  ;  calling  this  b,  we  have,  for  tan  AOB, 


tan  AOB  =,  +  - 

2v*  '   a 


in  which  the  second  member  is  known,  since  v  can  be  calcu- 
lated by  Exterior  Ballistics. 

If  the  shot  does  not  strike  vertically  above  By  there  will 

-ic 

be  a  lateral  deviation  ct  whose  measure  is  tan    —  . 

a 

If  OB  is  not  horizontal,  the  same  principle  applies,  the 
triangle  A  OB  being  an  oblique,  instead  of  a  right-angled  tri- 
angle. 

285.  Description  of  Sights  for  8,  10,  and  12  Inch  Seacoast  Guns. 

These  guns  have  two  sets  of  sights.  The  first  set,  AA't 
Fig.  276,  is  on  the  middle  element  of  the  reinforce,  and 
consists  of  a  simple  rear-sight  notch,  A,  and  a  conical  front 
sight,  Ar.  They  cannot  be  used  for  elevations,  and  are  for 
catching  the  target  readily,  and  giving  the  general  direc- 
tion. 


490 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


The    second    set,  BB ',    Fig.    276,   is  placed  on  the  left 
side  of  the  gun,  as  shown,  and  are  on  this  side  so  as  to  be 


FIG.  276. 

out  of  the  way  of  loading,  and  so  that  the  gun  may  be 
sighted  while  the  charge  and  projectile  are  being  inserted. 

The  rear  sight,  Fig.  277,  slides 
through  a  bronze  socket,  C,  bolted  to 
the  breech-plate.  This  socket  is  in- 
clined to  the  left  at  the  permanent  drift 
angle,  which  is  2°  30'  for  the  8-inch  gun, 
2°  45'  for  the  lo-inch,  and  3°  oo'  for  the 
12-irich.  It  is  prolonged  upward  a  dis- 
tance ab,  to  give  increased  support  and 
steadiness  to  the  sight. 

The  socket  carries  a  worm,  c,  which 
engages  in  a  corresponding  thread,  </,  in 
the  right-hand  edge  of  the  sight.  This 
worm  is  worked  by  a  hand-wheel,  e,  and 
pinion,  /,  and  the  hand-wheel  e  is  held 
in  place,  and  motion  prevented,  by  a 
clamping-wheel,  e" .  The  functions  of 
the  worm  are  to  raise  and  lower  the  rear 
sight,  and  to  hold  it  fixed  in  any  given 
position,  so  that  it  will  not  be  moved  by 
the  shock  of  firing. 

The  sight  consists  of  a  hollow  steel 
bar,  B,  one  inch  square,  graduated  in 
degrees,  and  each  degree  into  six  parts. 
The  smallest  reading  on  the  sight  is 
therefore  10  minutes.  The  top,  a,  of  the 
divided  into  10  equal  parts,  and  the 


FIG.  277. 
bronze  socket,  C,  is 


POINTING— PROBABILITY   OF  FIRE.  49! 

divisions  on  the  sight  are  diagonal,  so  that  by  means  of  the 
scale  on  the  socket,  each  of  these  graduations  on  the  sight, 
can  be  divided  into  ten  equal  parts,  giving  one  minute  for 
the  least  reading. 

The  top  or  head  of  the  sight,  consists  of  a  deflection-bar, 
g,  with  a  vertical  projection,  carrying  a  notch,  i,  and  a  peep- 
sight,  2.  The  notch  is  used  in  connection  with  the  top  of 
the  front  sight,  to  catch  the  target  quickly,  and  the  peep- 
sight  with  the  cross  wires  of  the  front  sight,  for  final  adjust- 
ment. The  deflection-bar,  £-,  has  a  horizontal  sliding  motion 
through  the  top  of  the  rear-sight  bar,  to  correct  for  wind, 
drift,  and  other  errors,  and  is  clamped  in  any  position  by 
the  clamp-screw  h.  It  is  graduated  as  shown,  each  gradua- 
tion being  y^  o"  °f  tne  range. 

For  deflection  to  the  left,  the  bar  is  used  in  the  position 
shown.  For  deflection  to  the  right  the  small  pin  x  is  pushed 
in,  the  bar  entirely  removed  from  its  socket,  and  reinserted 
from  the  right,  the  graduations  being  the  same  on  the  re- 
verse side. 

The  right-hand  side  of  the  sight-bar,  contains  a  portion, 
of  a  screw-thread  d,  into  which  gears  the 
worm,  c,  for   raising  and   lowering,  as 
before  explained. 

The  front  sight  B' ,  Fig.  278,  consists 
of  two  truncated  cones,  with  the  smaller 
bases  together  at  the  middle,  and  carry- 
ing two  flat  steel  cross  ribbons,  w,  halved 
into  each  other.  It  has  also  a  top  sight  FlG-  278- 

/,  which  is  used  with  the  open  notch  of  the  rear  sight  B. 

286.  Gunner's  Quadrant  for  Mortars. 

When  the  angle  of  elevation  exceeds  15°,  the  rear  sight 
above  described,  becomes  so  long  as  to  be  difficult  to  handle 
and  it  may  bend  under  its  own  weight,  so  as  to  cause  in- 
accuracy in  aiming. 

The  target,  also,  in  such  cases,  is  not  generally  visible  from 
the  gun  or  mortar,  and  for  these  reasons  the  rear  sight  is 
not  used.  To  give  the  necessary  elevation  in  such  cases, 
and  for  mortar-fire  generally,  the  gunner's  quadrant  is  used. 


492 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


This  consists,  Fig.  279,  of  the  body  a,  and  a  movable 
arm,  b. 

The  body  is  made  of  bronze,  and  carries  an  arc  graduated 
on  one  side  from  o°  to  44°,  and  on  the  opposite  side  from 
45°  to  89°.  On  the  inside  edge  of  the  graduated  arc  are 


FIG.  279. 

teeth  c,  each  of  which  corresponds  to  one  degree.  An  arrow 
is  marked  on  each  side  of  the  body,  and  when  the  quadrant 
is  in  use,  the  arrow  on  the  side  on  which  the  reading  is  taken 
must  always  point  in  the  direction  of  the  target. 

The  movable  arm,  b,  is  pivoted  to  the  body  at  d. 

This  arm  has  a  small  toothed  sector,  e,  which  is  acted  on 
by  a  spiral  spring,  contained  in  the  arm,  and  by  which  the 
sector  is  pressed  outward,  so  that  its  teeth  will  remain 
engaged  with  those  of  the  graduated  arc.  The  upper  sur- 
face of  the  movable  arm,  b,  is  the  arc  of  a  circle,  and  on  this 
arc  rests  a  level,  /.  This  level  bears  on  the  arm  at  two 
points  only,  and  is  of  such  a  length  that  when  moved  along 
the  arc  from  its  zero-point,  to  its  extreme  position  at  the 
other  end  of  the  arm,  the  angle  moved  over  is  one  degree. 

The  arm  is  graduated  in  minutes. 

Degrees  are  read  on  the  graduated  arc,  and  minutes  by 
the  scale  on  the  movable  arm. 


POINTING— PROBABILITY   OF  FIRE. 


493 


To  Use  the  Quadrant. — Suppose  the  elevation  to  be 
20°  1 8'. 

Press  back  the  toothed  sector,  e,  and  move  the  arm,  by 
till  its  index  is  opposite  the  20°  mark  on  the  graduated  arc. 

Slide  the  level,/,  along  the  movable  arm,  b,  till  its  index 
is  opposite  the  18'  mark  on  the  arm.  The  quadrant  is  now 
set  to  20°  iS'. 

Place  the  side,  ;#«,  on  the  flat  surface  prepared  for  it,  near 
the  breech  of  the  gun,  or  the  side,  m'  ri ,  against  the  face  of  the 
muzzle,  being  careful  to  keep  the  side  on  which  the  reading 
is  taken,  to  the  left,  and  the  arrow,  0,  pointing  toward  the 
target.  Elevate  the  piece  till  the  bubble  in  the  level  comes 
to  rest  in  the  centre.  For  any  elevation  greater  than  45°, 
as  60°  33',  use  the  graduations  on  the  other  face  of  the  arc, 
and  the  scale  on  the  movable  arm  as  above. 

The  other  side  of  the  quadrant  must  now  be  turned  to 
the  left,  and  the  arrow  on  it  pointed  toward  the  target. 
Elevate  the  gun  as  before. 

287.  Sights  for  Siege  Artillery — For  7-inch  Howitzer. 

The  sight  for  the  5-inch  siege-gun,  is  exactly  similar  to 
that  for  the  3.2  field-gun  to  be  described.  That  for  the 
7-inch  mortar  is  the  gunner's  quadrant  already  described. 

SIGHT  FOR  /-INCH  HOWITZER. — This  piece  has  a  com- 
paratively low  initial  velocity,  and  curved  fire.  Hence  the 
sight  for  this  gun  should  give  a  large  scale  for  correcting 
lateral  deviations,  as  they  will  be  greater  than  for  the  siege- 
gun,  which  has  a  high  velocity. 


FIG.  280. 

Being  fired  from  a  fixed  platform,  the  inclination  of  the 
trunnions  may  be  neglected,  in  comparison  with  the  errors 
due  to  low  velocity,  and  hence  the  standard  does  not  rotate 


494 


TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 


about  its  zero-point,  so  as  to  remain  always  in  a  vertical 
plane. 

For  the  5-inch  siege-gun,  its  high  velocity  renders  it 
more  accurate,  and  although  it  is  fired  from  a  fixed  plat- 
form, and  the  inclination  of  the  trunnions  is  consequently 
small,  any  error  due  to  this  cause  is  eliminated  by  the  rota- 
tion of  the  rear-sight  standard. 

Position. — The  sights  for  the  /-inch  Howitzer,  (Fig.  280), 
are  placed  on  the  right  side  of  the  piece,  the  rear  sight,  A, 
in  a  hole  drilled  through  the  rear  end  of  the  jacket,  and  the 
front  sight,  B,  on  the  right  rim-base. 

The  Rear  Sight.— A  hole,  (Fig.  281),  is  drilled  in  the 
jacket,  in  which  fits  a  socket,  b, 
held  in  place  by  a  set-screw,  c.  The 
sight  is  a  round  steel  rod,  a,  made 
flat  on  the  rear  side,  which  con- 
tains the  graduations  in  degrees, 
and  the  usual  diagonal  scale. 

This  rod  fits  accurately  in  the 
socket  b,  and  carries  a  sliding  collar, 
.d,  (Figs.  281  and  282),  which  may  be 
fixed  at  any  point  along  the  scale 
by  the  clamp-screw,  e.  The  rear 
upper  edge  f  of  this 
bevelled,  and  carries  a 
means  of  which  the 
diagonal  divisions  may 
be  read  to  I  minute. 

The  bottom  of  this 
collar  has  two  projec- 
tions, n,  diametrically 
opposite.  These  fit 
into  corresponding 
notches,  n'  (Fig.  282), 
in  the  top  of  the  socket 
b. 

The   axis   of   these 

FlG-  28r-  notches  is  at  right  an- 

gles to  the  axis  of  the  bore,  and  they  are  so  arranged  that 


collar   is 
scale   by 


POINTING— PROBABILITY   OF  FIRE. 


495 


0 


u 


the  sight  may  be  inserted  into  the  socket  for  a  reading  of 
the  deflection-bar  to  the  right,  or  by  lifting  the  sight  and 
turning  it  180°  about  its  axis,  the  sight  may  be  reinserted  in 
the  socket,  and' the  deflection-bar  can  be  read  to  the  left. 
The  correction  for  lateral  deviation  is 
given  by  a  deflection-bar,  h  (Fig.  281), 
sliding  in  a  socket,  g,  on  the  top  of  the 
rear  sight-bar,  and  clamped  in  any  posi- 
tion by  the  clamp-screw  i.  It  is  gradu- 
ated similarly  on  both  sides,  and  by 
turning  the  sight  180°,  as  previously  ex-  FlG-  283- 

plained,  deflections  may  be  read  to  the  right  or  to  the  left. 
A  vernier,  v,  on  the  right  edge  of  the  socket,^,  enables  the' 
divisions  on  the  deflection-bar  to  be  read  to 
-jL-  of  the  scale,  the  vertical  divisions  on  this 
bar  being  y^  of  the  range.  The  deflection- 
bar  is  provided  with  two  movable  sight- 
pieces,  r  and  u  (Figs.  281  and  283),  fitting  into 
a  socket,  s,  on  the  deflection-bar,  and  held  in 
place  by  a  clamp-screw,  /.  For  direct  pointing 
the  sight  piece,  r,  is  placed  in  its  socket  in  the 
deflection-bar,  and  u  in  the  front-sight  socket. 
For  indirect  pointing  upon  an  object  in  rear, 
when  the  target  is  not  visible,  the  sight- 
pieces  r  and  u  are  interchanged. 

Front    Sight. — The    front    sight    consists 
(Fig.  284)  of  a  base,#,  fastened  to  the  rimbase 
by  four  screws. 
The  top  is  provided  with  a  socket  of  the  same  shape  and 
dimensions  as  that  of  the  deflection-bar  h  (Fig.  281).      The 
thumb-screw  */ clamps  the  sighting-piece  firmly  in  position. 

288.  Sights  for  Field  Artillery— 3.6  Mortar— 3.2  Field-gun. 

SIGHTS    FOR   3.6    MORTAR. — The  sights  for  this  piece 


FIG.  284. 


FIG,  285. 


49<5 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


(Fig.  285)  are  a  notch,  A,  in  rear,  and  a  point,  B,  in  front, 

near  the  muzzle. 

SIGHTS  FOR  3.2  FIELD-GUN. — The  rear  sight  consists  of 

a  base,  A,  Fig.  286,  which  fits  in  a  corresponding  socket  in 

the  gun ;  a  pivot,  B,  Fig.  287, 
which  fits  into  the  bearing  &t 
Fig.  286,  of  the  base,  and  ro- 
tates around  the  bearing  b, 
Fig.  287 ;  and  a  standard,  C, 
Fig.  288,  carrying  the  gradua- 


FIG.  286.  FIG.  287. 

tions.  The  pivot  B,  Fig.  287,  has  two  cuts,  c,  c' ,  of  the  shape 
shown,  in  which  slide  corresponding  projections,  c,  c' ,  Fig. 
288,  of  the  standard. 

The  cylindrical  part,  b,  of  the  pivot,  B,  is  held  in  place 


FIG.  288. 


in  the  base  A,  Fig.  286,  by  two  screws,  a,  a',  passing  through 


POINTING— PROBABILITY   OF  FIRE. 


497 


the    side    of    the    base.     These    screws   enter    slots,   a,   a', 
Fig.  287,  in  the  pivot  B,  and  allow 
a  certain  amount  of  rotation  to  the 
pivot. 

The  standard  which  carries  the 
graduations  consists  (Fig.  288)  of 
an  upright  bar,  C ;  a  sliding-piece, 
D,  moved  up  and  down  along  the 
bar,  C,  by  a  screw,  d,  and  carrying 
the  peep-sight,  d' \  a  cross-bar,  e, 
carrying  the  graduations  for  lateral 
deflection  ;  a  screw,  /,  working  in  a 
half-nut,  /,  in  the  pivot  B,  Fig. 
287,  by  means  of  which  the  stand- 
ard is  moved  to  the  right  or  left; 
a  spirit-level,/,  which  indicates  the 
vertical  position  of  the  standard; 
and  two  projections,  c,  c' ,  which  fit 
in  the  corresponding  cuts,  c,  c',  in 
the  pivot  B. 

The  axis  of  rotation  is  at  the 
zero  of  the  scale,  and  the  usual 
diagonal  scale,  divided  into  10- 
minute  intervals,  is  read  to  one 
minute,  by  a  scale  on  the  sliding- 
piece  D. 

The  assembled  sight  is  shown  in 
Fig.  289,  and  its  action  is  evident.  FIG.  289. 

Front  Sight. — This    consists   (Fig.    290)   of    a   base, 
c  ^£^~e 

\r~d 


__- 

- 

—  ,-, 

_-•*—. 

c 

(/) 

r 

b 

a 


FIG.  200. 


bolted  to  the  right  rim-base  ;  a  standard,  b  ;  and  a  cylinder,  c. 


49^ 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


These  are  all  formed  in  one  piece.  The  cylinder  carries 
two  thin  cross  ribbons  of  steel,  d,.in  an  inner  cone,  c',  and 
a  front  sight-point,  e.  The  point  e  and  top  of  slide  d" , 
Fig.  289,  are  used  for  coarse  sighting,  while  the  cross- 
ribbons  and  peep  are  for  fine  sighting. 

The  sights  are  on  the  right  side  of  the  piece.  That  for 
the  3.6-gun  is  similar. 

289.  Deviations — How  Measured. 

DEVIATIONS. — Owing  to  the  causes  previously  explained, 
if  a  series  of  shots  be  fired  at  a  given  point  of  a  target,  they 
will  in  general  not  hit  the  point  aimed  at,  nor  will  they  be 
grouped  symmetrically  around  this  point.  Each  shot  will 
have  a  trajectory  differing  from  the  other  shots,  and  all 
these  trajectories  taken  together  will  form  a  sheaf  of 
trajectories,  whose  shape  in  general  is  that  of  a  bent 
cone.  The  axis  of  this  cone  is  called  the  mean  trajectory, 
and  all  the  others  are  grouped  symmetrically  about  it. 
The  point  where  this  axis  pierces  the  target  is  called  the 
centre  of  impact,  and  the  distance  of  this  centre  of  impact 
from  the  point  aimed  at,  is  called  the  mean  deviation.  In 
Fig.  291  let  O  be  the  point  aimed  at;  AC  the  axis  of  the 

a 


FIG.  291. 

sheaf  of  trajectories  ;  C  the  point  where  this  axis  or  mean 
trajectory  pierces  the  plane  of  the  target.  Then  C  is  the 
centre  of  impact,  and  OC  the  mean  deviation. 

How  MEASURED. — It  is  usual  to  measure  deviations  in 
three  directions : 

1.  In  the  direction  of  the  range; 

2.  Laterally,  in  the  direction  ab\ 

3.  Vertically,  in  the  direction  ac. 

For  the  mean  range  deviation  the  target  is  usually  taken 


POINTING— PROBABILITY  OF  FIRE. 


499 


horizontal,  and  the  measurements  made  from  the  centre  of 
the  target,  in  the  direction  of  the  range.  In  case  a  hori- 
zontal target  cannot  be  used,  the  mean  range  deviation  may 
be  obtained  from  the  mean  vertical  deviation,  by  considering 
that  part  of  the  mean  trajectory,  CD,  in  rear  of  the  target  to 
be  a  straight  line,  making  an  angle  GO  with  the  horizontal 
equal  to  the  angle  of  fall.  This  angle  can  be  calculated  by 
the  formulas  of  Exterior  Ballistics. 
We  have  then 

D'D  =  CD'  cotang  GO  ; 

or,  if  the  mean  range  deviation  is  measured  on  a  horizontal 
target,  we  have  for  the  mean  vertical  deviation 

CD'  =  DD'  tan  GO. 

The  same  method  applies  to  any  shot  of  the  sheaf  of 
trajectories.  The  mean  lateral  deviation  is  measured  parallel 
to  ab,  and  is  OD'  in  the  figure,  and  the  mean  vertical  devia- 
tion is  measured  parallel  to  ac,  and  is  CD'  in  the  figure. 
The  lateral  and  vertical  deviations  of  any  shot  are  measured 
in  the  same  way,  from  the  point  aimed  at,  to  the  centre  of 
the  shot-hole. 

290.  To  Find  the  Centre  of  Impact— Example. 

In  order  to  measure  the  mean  deviations,  it  is  necessary 
to  determine  the  position  of  the  centre  of  impact.  For  this 
purpose,  in  Fig.  292,  assume  an  origin  of  co-ordinates  at  the 


ok- 


FIG.  292. 

lower  left-hand  corner  O  of  the  target,  and  axes  OX  in  the 
direction    of    the  range,   OY  laterally,  and   OZ  vertically. 


500  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  point  O  is  selected  as  an  origin,  for  convenience,  to 
avoid  the  use  of  negative  co-ordinates. 

Let  #',  #",  etc.,  denote    the   distances  of  the  shot-marks 

from  O  measured  parallel  to  OX\ 
y,y,  etc.,  parallel  to  <9F; 
z' ,  z" ,  etc.,  parallel  .to  <9Z; 

X ',  F ',  Z' ',  the  co-ordinates  of  the  point  aimed  at; 
^f,  F,  Z,  the  co-ordinates  of  the  centre  of  impact ; 
w,  the  number  of  shots. 
Then 

g/       *>       x>>>       etc. 


n 

7        *'  +  z"  +  z'"  +  etc. 
n  ; 

and  the  point  whose  co-ordinates  are  (XY)  in  the  horizontal 
plane,  and  (FZ)  in  the  vertical  plane  will  be  the  centre  of 
impact. 

The  mean  deviations  in  range,  laterally  and  vertically, 
will  then  be 

In  range  X  —  X' ; 
Laterally  F-  F; 
Vertically  Z  -  Z '. 

Similarly  for  any  shot  the  deviations  in  range,  laterally 
and  vertically,  will  be 

In  range  x'  —  X' ; 
Laterally  /  —  F' ; 
Vertically  z'  —  Z '. 

In  these  calculations  the  positive  sign  indicates  distances 
beyond,  to  the  right,  and  above  the  centre  of  impact ;  the 
negative  sign  distances  short  of,  to  the  left,  and.  below  that 
centre. 

EXAMPLE.— Eight  shots  are  fired  from  the  3.2o-inch  steel 
field-gun  at  a  vertical  target,  range  1760  yards. 


POINTING— PROBABILITY  OF  FIRE. 


501 


Size  of  target  40  by  20  feet.  The  co-ordinates  of  the 
shots,  measured  from  the  lower  left-hand  corner  of  the  target, 
are  as  given  in  the  table. 

Find  the  mean  deviation  in  range,  laterally  and  verti- 
cally, or  the  co-ordinates  of  the  centre  of  impact. 


TABLE. 


No.  of  Shots. 

Co-ordinates,  feet. 

Lateral. 

Vertical. 

I 

2 

3 

9-00 
21.68 
14.25 

9.50 
5.OO 
5.66 

4 
5 
6 

17.00 
II.OO 
19.00 

5.00 

8.66 
9.82 

7 
8 

I7.OO 
14.83 

10.32 
9.00 

8)12376 

8)62.96 

Y=  1547 

Z=7.S7 

The  co-ordinates  of  the  centre  of  the  target  are 
Y'  =  20,     Z'  =  10. 

Hence  the  mean  lateral  and  mean  vertical  deviations 
are: 

Mean  lateral        Y—  Y'  —  —  4.53  feet  left; 
Mean  vertical    Z  —  Z'   =  —  2.13  feet  below. 

'The  mean  deviation  in  range  must  be  calculated. 

In  Fig.  293  OA  is  the  vertical  height  of  the  point  aimed 
at,  10  feet.  Assume  the  angle  of  fall  for  this  range  and 
elevation  GJ  =  3°.oo,  which  is  very  nearly  correct. 

The  centre  of  impact  C  is  below  the  point  O,  2.13  feet. 
Find  first  the  point  B,  which  is  the  position  of  the  centre  of 


502 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


the  target  O  on  the  horizontal  plane  ;  then  C ',  that  of  the 
centre  of  impact;  and  the  difference  C'B  is  the  mean  error 
in  range. 
We  have 

AB  —  10  X  cotan  3°  =  190.8  feet  =  63.6  yards  —  X' \ 

AC'  —  (10  —  2.13)  X  cotan  3°  =150.1  feet  =  50.03  yards  =  X. 

Mean  deviation  in  range  X  —  X'  —  —  40.7  feet 

—  1 3' 5^  yards  short. 
Mean  range  1760  -  13.56  =  1746.44  yards. 


C' 


FIG.  293. 


291.  Errors. 

The  centre  of  impact,  as  its  name  indicates,  is  the  centre 
of  the  group  of  shots  fired,  and  all  the  shot  are  grouped 
symmetrically  about  it.  Hence,  if  this  point  be  taken  as  a 
new  origin  of  co-ordinates,  for  every  positive  abscissa  or 
ordinate,  there  must  be  a  corresponding  negative  one,  and 
the  algebraic  sums  of  the  abscissas  or  ordinates  measured 
from  this  point,  are  equal  to  zero. 

The  abscissa  or  ordinate  of  any  shot  measured  from  the 
centre  of  impact  is  called  the  error.  Corresponding  to  the 
case  of  deviations,  errors  are  measured  in  three  directions : 
along  the  range,  laterally,  and  vertically.  The  distinctions 
between  deviations  and  errors  are : 

1.  Deviations  are    measured  from  the    point  aimed  at ; 
errors,  from  the  centre  of  impact. 

2.  Deviations  are  not  grouped  symmetrically  about  the 
point  aimed  at  unless  this  point  coincides  with  the  centre  of 


POINTING—  PROBABILITY  OF  FIRE.  503 

impact,  while  errors  are  grouped   symmetrically  about  the 
latter  point. 

It  is  theoretically  possible,  by  carefully  correcting  for 
wind,  drift,  and  the  various  other  causes  before  enumerated, 
to  make  the  centre  of  impact  coincide  with  the  point  aimed 
at,  and  the  mean  trajectory  pass  through  that  point.  But 
when  this  has  been  done  the  trajectories  will  still  form  a 
sheaf  or  cone  about  the  mean  trajectory  as  an  axis.  This  is 
due  to  accidental  errors  which  cannot  be  corrected,  and 
whose  consideration  requires  the  application  of  the  doctrine 
of  probability,  to  be  discussed  later. 

To  find  the  error  of  any  shot,  and  the  mean  errors  for  n 
shot,  we  have  given  the  co-ordinates  of  the  shot  and  those 
of  the  centre  of  impact,  referred  to  the  origin  at  the  lower 
left-hand  corner  of  the  target. 

Let  X,  Y,  Z  be  the  co-ordinates  of  the  centre  of  impact  ; 
x'j  y'  ,  z'  ,  those  of  a  shot  ; 
ex,eyl  ex,  the  errors  in  the  directions  X,  Y,  Z,  respect- 

ively for  each  shot  ; 
e*,  €yt  e,,  the  mean  errors  in  range,  laterally  and  ver- 

tically respectively,  for  n  shot. 
Then 

ex  =  ^  -  X, 


and 

4.      ,/       ,"      etc. 


_  ez  +  e,'  +  e,"  +  etc. 


n 


The  sums  ex  +  ex  +  etc.,  ey  +  ey  +  etc.,  e,  -f-  */  +  etc.,  if 
taken  with  their  proper  signs,  are  each  equal  to  zero,  accord- 
ing to  the  principle  previously  explained.  Hence,  in  adding 
these,  they  must  be  taken  without  regard  to  sign,  and  the 
sum  of  their  numerical  values  obtained.  For  instance,  if 


504 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


two  shots  are  fired,  and  one  strikes  10  feet  beyond  and  the 
other  10  feet  short  of  the  centre  of  impact,  the  values  of 
ex  and  ex  will  be  +  IO  and  —  10,  respectively,  and  this  sum, 
considering  the  signs,  is  zero. 

But  the  total  error  committed  in  this  case  is  20  feet  for 
the  two  shots,  and  hence  the  mean  error  is  %£-  =  10. 

The  error,  measured  from  the  centre  of  impact  directly 
to  a  shot,  is  called  the  absolute  error.  Denoting  this  error 
by  r,  we  have 


r  — 


or     = 


and  the  mean  absolute  error  is 


292.  EXAMPLE. — Find  the  errors  laterally  and  vertically 
and  the  mean  errors  for  the  3.2O-inch  field-gun  with  the 
data  in  the  last  example. 


TABLE. 


Co-ordinates  —  Feet. 

Errors  —  Feet. 

Squares  of  Errors. 

No. 

Shots. 

Lateral. 

Vertical. 

Lateral. 

Vertical. 

Lateral. 

Vertical. 

I 

9.0O 

9.50 

~  6.47 

+  1-63 

41.8609 

2.6596 

2 

21.68 

5.00 

+  6.21 

-2.87 

38.5641 

8.2369 

3 

14.25 

5.66 

—  1.22 

—  2.21 

1.4884 

4.8841 

4 

17.00 

5.00 

+  i-53 

-2.87 

2.3409 

8.2369 

5 

11.00 

8.66 

-447 

+  0-79 

19.9809 

0.6241 

6 

19.00 

9.82 

+  3-53 

+  i-95 

12.4609 

3-8025 

7 

17.00 

10.32 

+  1-53 

+  245 

2.3409 

6.0025 

8 

14.83 

9.00 

—  0.64 

+  1.13 

0.4096 

1.2769 

123.76 

62.96 

25.60 

15.90 

2ey*=  1  19.4466 

2^a  =  35.72o8 

F=i547 

Z=7.87 

6^=3.20 

€,=  1.9875 

It  will  be  observed  that  the  positive  and  negative  lateral 
errors  balance  each  other,  and  also  the  positive  and  nega- 
tive vertical  errors,  as  they  should  do,  for  the  reasons 


POINTING— PROBABILITY   OF  FIRE.  505 

already  explained.  Also,  that  the  sum  of  the  positive  or 
the  negative  errors  in  either  column,  divided  by  one  half 
the  number  of  shots,  will  give  the  correct  values  of  ey 
•and  ez. 

To  calculate  the  range  errors  and  the  mean  error  in 
range,  the  same  principle  applies  as  for  deviations,  that  is, 

ex  =  ez  cotan  GO, 
ex  —  ez  cotan  GO. 

In  our  service  a  different  mean  absolute  error  is  some- 
times used  as  a  measure  of  the  accuracy  of  a  gun.  It  is 
taken  as  the  hypothenuse  of  a  right-angled  triangle  of 
which  the  other  two  mean  errors  are  the  sides.  Thus  for 
the  3.2O-inch  gun  in  the  example  the  mean  absolute  error  is. 


em  =  Ve;  +  6,'  =  V(3.20)<  +  (1.9875)'  =  3-77  feet. 

This  differs  slightly  from  the  true  mean  absolute  error  er 
previously  explained,  which  would  be  in  this  case  4.003  feet. 


PROBABILITY  OF   FIRE. 

293.  Division  of  Sheaf  of  Trajectories— Law  of  Error — Probability 
Curve — Principles  upon  which  Form  of  Curve  Depends. 

DIVISION  OF  TRAJECTORY. — Considering  the  errors  in  a 
given  number  of  shots,  it  is  found  that  they  vary  in  magni- 
tude according  to  a  certain  law.  As  we  approach  the  centre 
of  impact  the  shot-marks  become  more  numerous,  and  as  we 
recede  from  it  they  decrease  in  number.  That  part  of  the 
sheaf  of  trajectories  which  contains  one  half  the  whole  num- 
ber of  shots  is  called  the  "  nucleus  "/  outside  of  the  nucleus, 
the  surrounding  part,  containing  40  per  cent,  is  called  the 
"envelope" ;  and  outside  of  this,  the  remaining  10  per  cent  is 
called  the  u  tailings" 

LAW  OF  ERROR. — Since  one  half  the  shot  are  grouped 
within  a  small  distance  of  the  centre  of  impact,  it  may  be 
inferred  that  small  errors  are  more  apt  to  occur  than  large 
ones  ;  and  since  only  10  per  cent  of  the  shot  lie  at  any 
considerable  distance  from  the  centre  of  impact,  it  may  be 


506 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY 


inferred  that  the  chances  of  committing  large  errors  are 
small,  or  that  very  large  errors  are  not  likely  to  occur. 

PROBABILITY  CURVE. — This  law  is  general  and  applies 
not  only  to  errors  of  shot,  but  to  accidental  errors  ol  any 
kind.  It  may  be  expressed  by  a  curve,  called  the  proba- 
bility curve,  whose  form  is  shown  in  Fig.  294. 


a        O       & 

FIG.  294. 


X 


In  this  figure  let  O  represent  the  centre  of  impact,  and 
XX'  the  direction  of  the  range.  Let  Oa,  Ob,  Oc  represent 
errors  in  range,  their  magnitude  being  represented  by  the 
lengths  of  Oa,  Ob,  etc.,  measured  from  O.  Then  from  the 
law  of  error  it  is  evident  that  the  smaller  error  Oa  is  more 
likely  to  occur  than  the  larger  one  Ob,  and  this  latter  than 
the  larger  one  Oc. 

In  a  large  number  of  shots,  the  error  Oa  will  also  occur 
more  frequently  than  Ob,  and  so  on. 

If  in  10  shots  the  error  Oa  occurs  four  times,  Ob  three, 
and  Oc  once,  the  fractions 


measure  the  probability  of  the  occurrence  of  these  errors 
respectively. 

Hence  if  we  lay  off  errors  along  XX1,  measuring  from  O, 
and  at  the  points  a,  b,  c,  etc.,  erect  ordinates  proportional  to 
the  probability  of  the  corresponding  errors,  we  will  obtain 
the  curve  in  the  figure. 

The  same  discussion  applies  to  lateral  and  vertical  er- 
rors, as  they  follow  the  same  law. 

PRINCIPLES  UPON  WHICH  FORM  OF  CURVE  DEPENDS.  — 
The  form  of  the  curve  depends  upon  the  following  gen- 
eral principles  : 


POINTING— PROBABILITY   OF  FIRE.  507 

1.  The  number  of  shots  striking  at  O  will  be  greater 
than  at  any  other  point,  or  the  probability  of  the  error  zero 
will  be  greater  than  that  of  any  other  error,  and  hence  the 
maximum  ordinate  of  the  curve  will  be  at  O. 

2.  The    number   striking   in  the    vicinity    of  O  will  be 
greater  than  for  points  farther  to   the  right  and  left,  and 
hence   the    ordinates    of   the    curve    will    decrease    slowly 
near  O. 

3.  The  number  of  hits  will  decrease  rapidly  as  the  dis- 
tance to  the  right  and  left  of  O  increases,  and  hence  the 
ordinates  of  the  curve  will  decrease  rapidly  in  these  direc- 
tions. 

4.  For  great  distances  from  O,  corresponding   to  large 
errors,  the  ordinates  will  be  very  small,  since  great  errors 
are  not  likely  to  occur. 

5.  The   only  error  that  cannot  occur  is   one  infinitely 
great,  and  hence  the  ordinate  of  the  curve  becomes  zero  at 
an  infinite  distance,  or  the  axis  of  Jf  is  an  asymptote  to  the 
curve. 

6.  Since  the  shot  are  as  likely  to  fall  short  of  the  point  O 
as  beyond  it,  the  same  error  Oa  is  as  likely  to  occur  on  one 
side  of  O  as  on  the  other,  and  hence  the  curve  is  symmetri- 
cal with  respect  to  the  axis  OY. 

294.  Equation  of  the  Probability  Curve— Properties  of  the  Curve — 
Limits. 

EQUATION. — The  equation  of  the  probability  curve,  de- 
duced by  analytical  methods,  is  (see  Johnson,  equation  i) 

y=±*-»", (404) 

in  which  y  is  the  ordinate  of  the  curve  corresponding  to  the 

abscissa  x,  or  the  probability  of  the  error  x ; 
h  is  the  modulus  of  precision,  whose  meaning  and 
value  will  be  explained  ; 

7C=  3.I4I6; 

e  =  the  base  of  the  Napierian  system. 
PROPERTIES  OF  THE  CURVE. — Differentiating  equation 
(404)  twice,  we  have 


508  TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 

=  -**,-»*  .......   (405) 


--_e-"^(l-2h^),       .    .     .     (406) 
x  Vn 

From  equation  (405),  when  x  —  o,  we  have 

?=-> 

dx 
and  hence  the  tangent  at  y  is  parallel  to  the  axis  of  x. 


Placing  -     —  o,  we  have 
dx 

I  —  2^V  =  O, 

or 

^  =  ~\  .......    (407) 

h  \2 

hence  —  =y  passes  through  zero  and  changes  its  sign  for  the 

drsC 

value  of  x  given  in  equation  (407).  There  is  therefore  a 
point  of  inflection  for  the  curve  corresponding  to  this 
abscissa. 

LIMITS.  —  In  discussing  the  probability  of  making  an 
error,  it  is  usual  to  consider  this  error  as  lying  within  certain 
limits.  Hence  it  is  necessary  to  consider  the  area  bounded 
by  the  probability  curve,  the  axis  of  errors,  and  an}'  two 
ordinates  whose  abscissas  represent  the  limits  between 
which  the  given  error  lies.  The  area  so  determined  repre- 
sents the  probability  of  the  occurrence  of  the  error  within 
the  given  limits. 

The  general  expression  for  the  area  of  a  curve  is 

P  =  fydx. 
Replacing  y  by  its  value  from  (404),  we  have 

^dx  ......     (408} 


POINTING— PROBABILITY   OF  FIRE.  509 

The  axis  of  XX'  extends  to  infinity  in  both  directions  as 
explained  ;  hence  the  total  area  under  the  curve  will  be 
obtained  by  integrating  equation  (408)  between  the  limits 
+00  and  —oo.  That  is, 


Place 

hx  =  of,     .-.  dx  =  — ; 

hence 

e'^da (409) 


The  value  of  the  integral  between  limits  is,  from  calculus, 
f+"e-a*da  =  */n'J      .....     (410) 

ts  —  co 

hence  in  (409) 

P=l, 

or  the  total  area  under  the  curve  is  unity.  This  means  that 
it  is  certain  that  the  error  will  be  contained  between  -{-oo 
and  -co  . 

Similarly,  for  the  probability  that  an  error  shall  be  con- 
tained between  any  limits  +  x  and  —  x,  we  have 


Since  the  curve  is  symmetrical  with  respect  to  the  axis 
OY,  we  have 


x*j        2h    rx  -&w  j 

xdx=-—      ehxdx    .     .     (412) 

/Wo 


for  the  probability  that  the  error  shall  be  less  than  x  re- 
gardless of  its  sign. 


510  TEXT- BOOK  OF  ORDNANCE  AND    GUNNERY. 

295.  Modulus  of  Precision  h— Use  of  Table  L 
Assume,  equation  (404), 


The  smallest  possible  error  is  zero, 
the  above  equation,  we  have 


Making  x  =  o  in 


(413) 


for  the  probability  of  the  error  zero.  It  is  evident  that  this 
is  the  greatest  value  of  y,  and  gives  the  maximum  ordinate 
OY. 

Suppose  we  have  another  series  of  shots  for  which  the 
value  of  h  differs  from  that  for  the  first  series,  as  h'  —  2/1. 
Then  the  probability  of  the  error  zero  in  the  second  case 
will  be 


V* 


(414) 


and  the  ordinate  will  be  twice  that  in  equation  (413). 

That  is,  the  probability  of  the  error  zero  will  be  twice  as 
great  in  the  second  series  as  in  the  first.     As  the  accuracy 


increases  with  the  probability  of  making  no  error,  we  con- 
elude  that  the  second  series  of  shots  is  more  accurate  than 


POINTING—  PROBABILITY   OF  FIRE.  511 

the  first.     The  quantity  h  is  then  a  measure  of  the  precision 
of  the  shots,  and  hence  is  called  the  modulus  of  precision. 

If  we  construct  the  probability  curves  for  the  two  series 
of  shots,  since  the  areas  under  them  are  always  unity,  we 
will  have  those  represented  in  Fig.  295,  OY  representing 
the  maximum  ordinate  for  the  first  series  and  OY'  for  the 
second.  It  is  evident,  from  the  above  discussion  and  figure, 
that  for  the  same  error,  x,  the  curve  of  probabilities  will  vary 
with  the  modulus  h.  Hence  it  is  usual  to  change  the  form 
of  the  equation  for  probability,  so  as  to  introduce  h  as  a. 
factor  of  the  error  x,  and  hence  into  the  limit.  Equation 
(412)  is  therefore  generally  written 

e-h^d(hx)  .....     (415) 

The  values  of  P  for  different  values  of  hx  have  been  cal- 
culated and  tabulated,  and  are  given  in  Table  I.  The  value 
of  h  as  deduced  analytically  is 


(4i6) 


2^V  ' 

in  which 

n  is  the  number  of  shots  ; 

2e*,  the  sum  of  the  squares  of  the  errors  in  any  given 

direction. 

USE  OF  TABLE  I. — Let  it  be  required  to  find  for  the  3.20 
gun  the  probability  of  committing  a  lateral  error  less  than  2 
feet,,  at  a  range  of  i  mile. 

The  value  of  2ey*  for  this  gun  is  119.45  (see  example, 
Subject  292) ;  hence 


h  —  \  / —  .1711 ; 

V  2  x  119-45 

hx  =  .1711  X  2  =  .3422; 

Pfor  hx  =  .3422        =  .37155; 
P  =  about  TV  ; 

or  about  four  shots  in  ten  will  make  an  error  less  than  2  feet 
laterally,  at  one  mile  range. 


512  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

TABLE  I. 

PROBABILITY    OF    ERRORS, 


hoc 

f 

hx 

P 

hx 

P 

hx 

P 

hx 

P 

0.00 

0.00000 

0.40 

0.42839 

0.80 

0.74210 

1.20 

0.91031 

.60 

0.97635 

.02 

.02256 

.42 

•44747 

.82 

•75381 

1.22 

•9*553 

.62 

.97804 

.04 

.04511 

•44 

.46622 

.84 

.76514 

1.24 

.92050 

.64 

.97962 

.06 

.06762 

.46 

.48465 

.86 

.77610 

1.26 

.92523 

.66 

.98110 

.08 

.09008 

.48 

.50275 

.88 

.78669 

1.28 

.92973 

.68 

.98249 

.10 

.11246 

.50 

1 

.52050 

.90 

.79691 

1.30 

.93401 

.70 

•98379 

.12 

.13476 

.52 

•53790 

.92 

.80677 

1.32 

.93806 

.72 

.98500 

.14 

.15695 

•54 

•55494 

•94 

.81627 

1-34 

.94191 

•74 

.98613 

.16 

.17901 

.56 

.57161 

.96 

.82542 

1.36 

.94556 

.76 

.98719 

.18 

.20093 

•58 

.58792 

.98 

.83423 

1.38 

.94902 

•78 

.98817 

.20 

.22270 

.60 

.60386 

.00 

.84270 

1.40 

.95228 

.80 

.98909 

.22 

.24429 

.62 

.61941 

.02 

.85084 

1.42 

•95537 

.82 

.98994 

.24 

.26570 

.64 

•63458 

.04 

.85865 

1.44 

.95830 

.84 

•99073 

.26 

.28690 

.66 

.64938 

.06 

.86614 

•46 

.96105 

.86 

.99147 

.28 

.30788 

.68 

.66378 

.08 

•87333 

.48 

.96365 

.88 

.99216 

•3° 

.32863  : 

.70 

.67780 

.10 

.88020 

.50 

.96610 

1.90 

.99279 

•32 

.34912; 

.72 

.69143 

.12 

.88679 

•52 

.96841 

1.92 

.99338 

•34 

.36936 

•74 

.70468 

.14 

.89308 

•54 

.97058 

1.94 

.99392 

•36 

.38933 

•76 

.71754 

.16 

.89910 

.56 

.97263  i 

1.96 

•99443 

.38 

.40901 

.78 

.73001 

.18 

.90484 

.58 

•97455  j 

1.98 

.99489 

2.0 

•99532 

3-o 

.99998 

00 

1  .00000 

296.  Probable  Error — True  Mean  Error — Relation  between  Prob- 
able and  True  Mean  Errors. 

Among  the  errors  which  may  be  committed,  from  zero 
to  infinity,  there  are  two  whose  values  are  of  constant  use 
and  importance. 

These  are  the  probable  error  and  the  true  mean  error. 

PROBABLE  ERROR. — In  Fig.  296,  the  total  area  under  the 
probability  curve  being  unity,  if  the  abscissas  Op  on  each 
side  of  O  be  so  taken  that  the  area///'/  included  between 
the  curve,  the  ordinates//',  and  the  axis  XX'  is  equal  to  one 
half,  the  error  Op  is  called  the  probable  error.  That  is,  it  is 
the  error  whose  probability  is  one  halt,  or  the  error  which  is 
as  likely  to  be  exceeded  as  not.  For  example,  if  ten  shots  be 


POINTING— PROBABILITY  OF  FIRE. 


513 


fired,  and  O  be  the  centre  of  impact,  the  probability  is  that 
five  of  these  shots  will  strike  within  the  distance  Op  from  the 
centre  of  impact  and  the  other  five  at  a  greater  distance. 
It  is  to  be  noted  that  while  the  probable  error  is  Op,  it  may 


f      o      p 

FIG.  296. 

occur  on  either  side  of  O,  and  hence  it  must  be  measured  in 
both  directions  from  O. 

From  Table  I,  the  value  of  hx  for  P  =  %  is 

hx  —  0.4769. 

Hence,  calling  this  error  xp,  we  have 
_  0.4769 


Substituting  for  h  its  value  from  (416),  we  have 


>  =  0.6745.  7-^-. 

V   n  —  I 


TRUE  MEAN  ERROR. — The  mean  error  has  already  been 
calculated  for  the  3.2O-inch  gun  for  a  limited  number  of 
shots.  If  the  number  of  shots  be  increased,  a  different  value 
for  the  mean  error  would  be  obtained,  and  the  true  value  of 
this  mean  error  can  only  be  found  for  an  infinite  number  of 
shots  :  hence  the  name.  Since  it  is  impossible  in  practice 
to  fire  an  infinite  number  of  shots,  the  value  of  the  true 


514  TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 

mean  error  must  be  found  by  analytical  methods  from  the 
equation  of  the  curve.     This  method  gives  for  its  value 

.  '  X"  =  Yvn (4'9) 

Substituting  the  values  ol  n,  and  of  h  from  (416),  we  have 

xm  =  0.79788.  /-^-- (420) 

V  «  -  i 

Dividing  equation  (418)  by  (420),  we  have 

-^  =  0.8453;     •••*,  =  0.845  3*,,.    •     •     •     (421) 

•*»« 

297.  Probable   Zone— Examples— Comparison   of  Mean  and   True 
Mean  Errors. 

PROBABLE  ZONE. — The  probable  zone  is  one  which  will 
probably  contain  50  per  cent,  or  one  half,  the  total  number 
of  shots.  Hence  the  probability  for  this  zone  is  P  =  %. 
Now,  in  considering  the  probable  error,  it  was  shown  that 
it  measured  a  distance  on  each  side  of  the  point  of  impact 
within  which  one  half  the  whole  number  of  shots  would 
strike  ;  and  hence  if  we  lay  off  a  distance  on  each  side  of  the 
centre  of  impact  equal  to  the  probable  error,  and  draw 
through  the  points  thus  determined  two  lines  at  right  angles 
to  the  plane  of  fire  and  extending  indefinitely  in  both  direc- 
tions, these  lines  will  determine  a  zone  which  will  contain 
50  per  cent  of  the  shots. 


** 

FIG.  297. 


In  Fig.  297  let  O  be  the  centre  of  impact ;  xpOxp,  the  di- 
rection of  the  range,  or  line  of  fire;  Oxp,  measured  in  both 
directions  from  O,  the  probable  error.  Then  the  zone  de- 


POINTING—  PROBABILITY  OF  FIRE.  $1$ 

fined  by  the  parallel  lines  extending  to  infinity  in  both 
directions  is  called  the  probable  zone,  and  will  contain  one 
half  the  whole  number  of  shots  fired.  The  same  reasoning- 
applies  to  the  lateral  and  vertical  probable  zones. 

The  width  of  this  zone  is  twice  the  probable  error,  or 


/  2S  I  2e* 

i  X  0.6745^  —  —  =  i.349y  ^-j- 


(422) 


EXAMPLES.  —  Find  the  probable  error,  true  mean  error, 
and  probable  zone  vertically  for  the  3.2O-inch  gun  at  one 
mile  range. 

*>  =  o.6745y  _^-    =  0.6745^  1A^5    =  1.523  feet  ; 

*w  =  0.79788A/  -  ^-  =  Q.79788A/  ^^  =  1-802  feet  ; 
2xp  —  2  X  1.523  =  3.046  feet. 

The  same  method  will  give  the  corresponding  errors 
and  zones  laterally  and  in  range,  2f  differing  for  the  differ- 
ent directions. 

COMPARISON  OF  MEAN  AND  TRUE  MEAN  ERRORS.—  The 
true  mean  vertical  error  in  this  case  is  XM  =  1.802  feet,  while 
the  mean  error  as  obtained  from  eight  shots  is  (see  table) 
1.9875  feet.  Hence  the  mean  and  true  mean  errors  differ 
very  slightly,  and  with  a  large  number  of  shots  the  differ- 
ence would  be  still  less.  This  is  true  generally,  and  hence 
the  calculated  mean  error  may  be  used  instead  of  the  true 
mean  error  without  appreciable  error  in  the  result.  This 
leads  to  a  simple  method  of  calculating  probable  zones,  as 
follows  : 

From  (421)  we  have 

xp  =  0.845  3*M  ;    .-.  2*>  =  1.69*,,.  .    .    .    (423) 

Substituting  for  xm  the  calculated  mean  error  ex,  ey,  or 


5i6 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


-X' 


eg,  we  have  for  the  probable  zone  in  any  one  of  these  direc- 
tions : 

Range        2xp  —  1.69  X  ex\  } 

Lateral      2yp  =  1.69  X  ^;  v  .     .     .     .     (424) 

Vertical     2zp  =  1.69  X  e,.  ) 

298    25  per-cent  Rectangle— Probable   Rectangle— Rectangles  of 
any  Percentage. 

Let  O,  Fig.  298,  be  the  centre  of  impact,  XX'  the  50  per- 
cent zone  for  the  range,  YYf  the  50  per-cent  zone  laterally. 

The  intersection  of  these  zones 
will  form  a  rectangle  about  the 
centre  of  impact,  and  this  rect- 
angle will  contain  one  fourth  or 
25  per  cent  of  the  shots,  for 

.50X  .50  =  .25 

This  is  called  the  25  per-cent 
rectangle.     It   is    the    rectangle 
formed  about  the  centre  of  im- 
FlG-  298-  pact  by  the  intersection   of  the 

two  50  per-cent  zones ;  and  since  each  contains  50  per  cent 
of  the  shots  independently  of  the  other,  by  the  doctrine  of 
probability,  when  they  intersect,  their  common  part  will 
contain  a  percentage  equal  to  the  product  of  the  two. 

PROBABLE  RECTANGLE. — The  probable  rectangle  is  one 
which  is  formed  by  the  intersection  of  two  zones  of  equal 
probability,  and  which  will  probably  contain  50  per  cent  of 
the  shots.  That  is,  its  probability  is  P  =  £. 

Now  the  probability  of  any  rectangle,  as  illustrated  in 
the  case  of  the  25  per-cent  rectangle,  is  equal  to  the  product 
of  the  probabilities  of  the  two  zones  whose  intersection 
forms  the  rectangle ;  and  denoting  the  probabilities  of  these 
zones  by  P'  and  P"  respectively,  we  have 

P  =  P'  x  P". 

It  is  evident,  however,  that  there  are  an  infinite  number 
of  zones  whose  intersection  will  give  a  rectangle  having  the 
probability  P=%,  since  any  two,  the  product  of  whose  prob- 


POINTING— PROBABILITY   OF  FIRE. 


517 


^abilities  is  one  half,  will  fulfil  this  condition.  To  fix  the 
rectangle,  therefore,  we  impose  the  condition  that  the  prob- 
abilities of  the  two  intersecting  zones  shall  be  equal.  Sub- 
stituting in  the  above  equation  this  condition,  we  have 

i  =  V £  X  \f\, 

or  the  probability  of  committing  an  error  less  than  one  half 
of  either  side  of  the  rectangle  is  P'  =  P"  =  V%. 
For 

F  =  i/J  =  0.7071 

we  have,  from  Table  I, 

hx  —  0.7438 ; 


hence 


07438 
It     ' 


(425) 


Substituting  for  h  its  value  from  (416),  we  have 


/~^7~ 

=  I.0524/  -. 

V   n  —  I 


This  is  the  value  of  one  half  the  side  of  the  rectangle. 
Hence 


Calling  the  sides  of  this  rectangle  in  the  horizontal  plane 

Ax  and  Ayt  and  in  the  vertical  plane  Ay  and  At,  we  have 

i 


1x=2.io4\/^-; 
V   n  —  i 

4,  =  2.i04\/    — £-  ; 
V    n  —  i 


=  2.104 


.     (426) 


RECTANGLES  OF  ANY  PERCENTAGE. — By  similar  reason- 
ing we  can  find  the  probable  rectangle  which  will  contain 


5l8  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

any  given  percentage  of  shots.     For  instance,  required  the 
rectangle  which  will  contain  twelve  out  of  twenty   shots 
fired  from  the  3.2  gun  at  one  mile  range. 
We  have 

|-|  =  60  per  cent. 

The  probability  of  this  rectangle  must  then  be 

P=.6, 
and  hence  the  probability  of  its  sides  P'  —  V.6,  since 


From  Table  I  the  value  of  hx  corresponding  to 

P'  =  t/"6  =  .7746 
is 

hx  —  .8572  ; 
hence 

x  - 


Substituting  for  h  its  value  from  (416),  we  have 

TW 

=  \.2\2\       - 

V   n  —  I 


X 

and 

2X 


=  2.424\/  -  — , 

V   n  —  I 


;/  —  i 


/     — -— — — 

2Z  =  2.424\/  -—, 

V   n  —  i 


and  so  on  for  a  rectangle  of  any  percentage. 

299.  Examples  —  Measure   of  Accuracy  of  Guns  — Calculation  of 

Probable  Rectangle  from  Mean  Error. 

Find  the  25  per-cent  rectangle,  the  probable  rectangle, 
and  the  60  per-cent  rectangle  for  the  3.20  gun,  in  the  vertical 
plane,  at  one  mile  range. 


POINTING— PROBABILITY  OF  FIRE.  519 

1.  The  25  per-cent  rectangle  : 

The  probable  zone  vertically  is  (see  subject  297) 

22 p  ==•  3.046  feet. 
The  probable  zone  laterally  is 

V2ey*  /i  19.45 

^f-j:  =  i.349y  --y1  =  5-57  feet 

Hence  the  25  per-cent  rectangle  is 

3.046  x  5-57  =  l6-97  sq.  feet. 

2.  The  50  per-cent  rectangle  : 


/  ^ev  /II9-45 

Ay  =  2.io4\/  -    —  =  2.104*7  —  ~=  =  8.69  feet; 

4,  =  2.i04y  ^-^-  =  2.io4y  -^    =  4-75  feet 


Hence  the  50  per-cent  rectangle  is 
8.69  x  4-75  =  4I-31  sq 
3.  The  60  per-cent  rectangle  : 


/"SFr 

4  /  —  —  =  10. 
V  »  —  i 


2y  —  2.42447  -       -  =  10.01  feet; 

7  "^  c  * 

22  =  2.424*7  -      -  =    5.48  feet. 
\    n  —  i 

Hence  the  60  per-cent  rectangle  is 

10.01  X  5.48  —  54.82  sq.  feet. 

COMPARISON  OF  ACCURACY  OF  GUNS.— The  probable 
or  50  per-cent  rectangle,  is  generally  used  to  compare  the 
accuracy  of  different  guns,  and  may  be  taken  either  in  the. 
horizontal  or  in  the  vertical  plane.  For  small  arms  and 
high-power  guns  the  vertical  rectangle  is  the  more  accurate 
means  of  comparison.  It  is  evident  that  for  high-power 


520  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

guns,  with  flat  trajectories,  the  horizontal  rectangles  will  be 
larger  than  for  guns  with  high-angle  or  curved  fire.  Hence 
if  we  compare  guns  and  mortars  by  their  horizontal  rect- 
angles, the  mortar  will  appear  the  more  accurate.  On  the 
other  hand,  for  high-angle  or  curved  fire,  horizontal  targets 
should  be  used  as  a  means  of  comparison.  The  most  accu- 
rate method  for  all  guns  is  to  take  the  plane  of  the  target 
.at  right  angles  to  the  trajectory  at  the  point  of  impact,  but 
this  is  generally  impracticable. 

CALCULATION  OF  PROBABLE  RECTANGLE  FROM  MEAN 
ERROR.  —  The  mean  error  of  a  given  number  of  shots  may 
be  readily  obtained  as  previously  shown. 

For  the  side  of  the  50  per-cent  rectangle  we  have,  equa- 
tion (425), 


From  (417), 

*=^:     ........    (428) 

and  from  (421), 

*>  =  0.8453*..  ........     (429) 

Substituting  the  value  of  xp  from  (429)  in  (428),  we  have 

k  _  0.4769      t 
0.8453*"' 

and  this  value  of  h  in  (427)  gives 

Ax  =  2x  =  2.636  X  xm.       ....     (430) 

300.  Use  of  Probable  Error  in  Calculating  Probabilities—  Use  of 
Table  II—  Example. 

The  probable  error  is  generally  used  as  a  standard  of 
comparison  for  other  errors,  since  it  represents  an  error 
which  is  as  likely  to  be  exceeded  as  not. 

For  the  probable  error  we  have,  equation  (417), 

_  0.4769 
' 


POINTING— PROBABILITY  OF  FIRE. 


521 


Using  this  as  a  unit  of  comparison,  the  ratio  of  any  other 

error  x  to  this  is 

x  hx 

(43I) 


In  Table  I  we  have  given,  values  of  P  corresponding  to 
Jix,  or,  conversely,  values  of  hx  corresponding  to  P.  Divid- 
ing the  values  of  hx  in  Table  I  by  0.4769,  we  have  the  cor- 

*£ 

responding  values  of  —  . 
xp 

Finding  the  values  of  P,  from  Table  I,  corresponding  to 

these  values  of  —  ,  we  can  form  a  new  table,  giving  the  values 

xp 

of  P  corresponding  to  —  ,  or  the  values  of  —  corresponding 

xp  xp 

to  P. 

This  table  is  called  Chauvenet's  Table,  and  is  given 
below. 

TABLE  II. 

PROBABILITY   OF    ERRORS. 


P 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

0.0 

o 

.02 

.04 

.06 

.07 

.09 

.11 

.13 

•15 

•  17 

.1 

.18 

.20 

.22 

.24 

.26 

.28 

•30 

•32 

•34 

•  36 

.2 

•38 

.40 

•  41 

•43 

-45 

•47 

.49 

•53 

•55 

.3 

.61 

.63 

•  6S 

.67 

.70 

•72 

•  74 

.76 

.4 

.78 

.80 

.82 

.84 

.86 

•  89 

•91 

•93 

•95 

.98 

.5 

1.  00 

1.02 

1.04 

1.07 

1.09 

1.  12 

1.14 

1.17 

1.19 

1.22 

.6 

1.25 

1.27 

1.30 

1-33 

1.36 

1.39 

1.42 

1-45 

1.48 

I.5I 

.7 

1.54 

1.57 

1.  60   1.64 

1.67 

I.7I 

1-74 

1.78 

1.82 

1.86 

.8 

1.90 

1.94 

1.98  1  2.03 

2.08 

2.13 

2.18 

2.24 

2.30 

2-37 

.9 

2.44 

2.52 

2.60 

2.69 

2.78 

2.9I 

3-°4 

3.22 

3-45 

3.82 

USE  OF  TABLE  II — EXAMPLES. 

i.  Required  the  probability  of  committing  a  lateral  error 
with  the  3.2  gun,  at  i  mile  range,  of  less  than  4.354  feet. 

The  probable  error  laterally,  for  this  range,  is  2.785  feet, 
hence 

y  _  4-345  _  I    6 

y>     2.785 


$22  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

From  Table  II,  P  for  2-  =  1.56  is 

P=  0.707 1  =  i/JT 

2.  The  probable  lateral  error  of  the  3.2  gun  at  i  mile 
range  is  2.785  feet. 

The  probability  of  committing  an  error  less  than  x,  is 

/>  =  VJ  =  0.7071.     Find  the  value  of  x. 
From  Table  II,  for  P  =  0.7071  we  have 

'  =  1.56,     .-.  y  =  1.56  x  2.785  =  4.345  feet. 

301.  Probability  of  Hitting  any  Plane  Figure. 

By  the  previous  methods  it  has  been  shown  how  to  deter- 
mine the  sides  of  a  rectangle  which  will  contain  any  given 
percentage  of  shots.  By  the  use  of  Table  II  we  can  readily 
determine  the  probability  of  hitting  any  plane  figure  of  a 
given  size  and  shape. 

As  the  simplest  case,  consider  first  a  rectangular  object. 


A 

K" 

M 

1 

{ 

B 

TT" 

I 

ij 

ti 

\r 

L 

Y 

I 

JT'" 

O 

F 

a  * 

TT' 

rt 

h__. 

rt 

C 

K'" 

r 

FIG. 

?      f 

299. 

C 

D 

Let  O,  Fig.  299,  be  the  centre  of  impact,  OF  and  OZ  the 
rectangular  axes,  and  suppose  vertical  errors  to  be  measured 
along  OZ,  and  horizontal  errors  along  OY.  For  the  given 
gun  and  range,  the  probable  errors  horizontally  and  verti- 
cally will  be  known  by  firing  a  certain  number  of  shots  and 
calculating  the  probable  errors  by  equation  (418). 

I.  What  is  the  probability  of  striking  the  rectangle 
ABDC  ? 


POINTING—  PROBABILITY  OF  FIRE.  $2$ 

From  Table  II  we  find  the  probability  of  committing  the 
error  OG  by  taking  out  the  value  of  P  corresponding  to 


yp     y* 

From  the  same  table  we  find  the  probability  of  commit- 
ting the  error  OM  by  taking  from  this  table  the  value  of  P 
corresponding  to 

OM 


and  the  probability  of  hitting  the  rectangle  ABCD  is  the 
probability  of  committing  these  two  errors  simultaneously, 
or  the  product  of  the  above  separate  probabilities. 

2.  What   is   the   probability    of    striking    the    rectangle 
OGBMl 

From  the  fact  that  the  shot  are  grouped  symmetrically 
about  O,  owing  to  the  law  of  probability,  it  follows  that  the 
number  of  hits  in  OGBM  will  be  \  of  those  in  the  rectangle 
ABCD.  Hence  the  probability  of  hitting  the  rectangle 
OGBM  is  |  that  of  hitting  the  rectangle  ABCD. 

3.  What  is  the  probability  of  striking  within  OMKF  ? 
This  is  found  exactly  as  for  the  rectangle  OMBG,     Find 

from   Table  II  the  probabilities  corresponding  to  —  and 

yp 

—  -,  and  multiply  these  probabilities  together.     The  result 

will  be  the  probability  of  striking  within  the  rectangle 
K"KK'K'",  and  \  of  this  will  be  the  probability  required. 

4.  What  is  the  probability  of  striking  FKBG  ? 

It  is  the  difference  between  the  probabilities  for  OGBM 
and  OFKM,  which  have  already  been  found. 

5.  What  is  the  probability  of  striking  OGHL  ? 

Find  from  Table  II  the  probabilities  for  —  and  -  ;  mul- 

y*        ZP 

tiply  these  probabilities  together  and  take  J  of  the  prod- 
uct for  the  probability  required. 

6.  What  is  the  probability  of  striking  FGHI  ? 


524 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


It  is  the  probability  of  striking  OGHL  minus  the  proba- 
bility of  striking  OFIL. 

7.  What  is  the  probability  of  striking  IKBH  ? 

It  is  the  probability  of  striking  OMBG  minus  the  sum  of 
the  probabilities  of  striking  OGHL  and  LIKM. 

In  the  same  way  any  figure  may  be  divided  into  rect- 
angles, approximately,  whose  centres  coincide  with  the 
centre  of  impact. 

The  probability  of  striking  the  rectangles  or  parts  of 
rectangles  about  the  centre  of  impact  may  be  readily  calcu- 
lated by  Table  II,  and  the  probability  of  striking  those  parts 
whose  centres  do  not  coincide  with  the  centre  of  impact 
may  be  determined  by  subtraction. 

302.  Right-line  Method. 

The  area  under  the  probability  curve  being  unity,  and 
the  curve  being  symmetrical  with  respect  to  the  axis  OYy 


the  area  under  each  branch  is  £.  If  a  right  line  BC,  Fig. 
300,  be  drawn  so  that  the  area  of  the  triangle  OBC  =  J,  and 
the  abscissa  of  its  centre  of  gravity  be  at  a  distance  Om  from 
O,  equal  to  the  true  mean  error  xm<  then  the  right  line  BC 
may  be  substituted  without  appreciable  error  lor  the  prob- 
ability curve. 

In  this  case  the  greatest  possible  error  is  OC  and  the 
greatest  possible  ordinate  is  OB,  and  to  show  that  the  right 
line  may  be  substituted  for  the  curve  it  is  necessary  to 
prove : 


POINTING— PROBABILITY   OF  FIRE.  $2$ 

1.  That  the  probability  of  the  error  OC  does  not  differ 
sensibly  from  that  of  the  error  oo ,    which   is  the   greatest 
possible  error  in  the  case  of  the  probability  curve. 

2.  That  the  ordinate   OB  does  not  differ  sensibly  from 
the  maximum  ordinate  O Y  of  the  curve. 

i.  Probability  of  the  error  OC. 

Since  in  a  triangle  the  centre  of  gravity  is  situated  at  a 
distance  from  its  base  equal  to  £  its  height,  we  have 


oc= 

but,  from  (419), 

Om  =  xm  = 
hence 


and 


h  X  OC  =  hx  —  -4=  =  1.6925. 

VTT 


From  Table  I  the  value  of  P  corresponding  to  hx  =  1.6925 
is 

^=.983. 

j 

The  value  of  P  for  Ar  =  oo  is 

P=  1 .00, 

hence  the  probabilities  of  the  extreme  errors  in  the  two 
cases  are  as 

.983  :  i.oo. 

That  is,  out  of  100  shots  98  will  make  an  error  less  than  OC. 

2.  Value  of  the  ordinate  OB,  as  compared  with  OY.  The 
maximum  ordinate  OY  oi  the  probability  curve  is  found 
by  making  x  =  o  in  equation  (404).  The  value  thus  ob- 
tained is 


526  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

or  since 


we  have 


X 


(432) 


From  the  triangle  OBC,  since  its  area  is  J  and  its  base 
3^rw,  we  have 

i  _  ((9^X3-0. 
2"  2 

hence 

OB  =  jiht (433) 

Comparing  (432)  and  (433),  we  see  that  the  numerators  of 
the  values  of  OY  and  OB  are  the  same,  and  the  denomina- 
tors differ  but  slightly,  and  hence  OB  may  be  taken  for  OY, 
or  the  right  line  may  be  substituted  for  the  curve  without 
appreciable  error. 

303.  Value  for  Probability  by  the  Right-line  Method. 


In  Fig.  301  make 


Ox  =*; 

Om  —  xm  ; 

xx  —  p' . 


POINTING—  PROBABILITY  OF  FIRE.  $2? 

v'x" 

Then  the  area  OBC  -~~  = 


From  the  similar  triangles  OBC  and  xx ' C  we  have 
OB'.OC  ::  xx'  :  OC  -  Ox,     or    /  :  x"  : :  p'  :  x' '  —  x  ; 
hence 

/'  = xn         ; 

but 

hence 

pf=y  3^7 (435) 

Substituting  in  (434)  for  p'  its  value  from  (435),  we  have 
area  OBx'x  =  JL^-JL-^      .     .     .     (^6) 

Now  the  probability  of  an  error  less  than  Ox  =  x  is  the 
ratio  of  the  area  of  the  triangle  OBC  to  that  of  the  trape- 
.zoid  OBxx'\  hence,  dividing  (436)  by  the  area  of  the  triangle 


,  we  have 

2 


(437) 


In  this  equation,  having  the  value  of  the  true  mean  error 
given  by  the  equation  (420),  or  that  of  the  mean  error  ob- 
tained as  explained  from  a  number  of  shots,  we  can  find  the 
probability  of  any  error  x  without  using  the  probability 
tables. 

This  discussion  of  probability  may  be  extended  to  include 
the  methods  for  hitting  circles  or  ellipses,  and  also  for  de- 
termining the  number  of  shots  necessary  to  produce  a  given 
result,  such  as  to  make  a  breach  in  a  wall,  etc.,  but  the 
discussion  is  too  extensive  for  the  present  course. 


CHAPTER  IX. 

PORTABLE   ARMS. 

304.  Division  —  Hand  Arms  —  Cutting  Arms  —  Principles — Light 
Artillery  Sabre. 

DIVISION. — Portable  arms  are  those  which  are  carried  by 
the  individual  soldier,  and  are  divided  into — 

1.  Hand  arms. 

2.  Small  arms. 

HAND  ARMS  are  those  which  are  used  for  attack  and  de- 
fence at  very  short  distances,  and  are  divided  according  to 
their  mode  of  action  into  — 

1.  Cutting  arms. 

2.  Thrusting  arms. 

3.  Thrusting  and  cutting  arms. 

CUTTING  ARMS— PRINCIPLES. — A  cutting  arm  is  one 
which  acts  by  its  edge,  and,  being  used  entirely  against  ani- 
mate objects,  is  based  upon  the  following  general  principles: 

1.  Since  the  object  to  be  cut  is  elastic  and  fibrous,  the 
blow  must  be  struck  so  that  only  a  few  points  of  the  cutting 
edge  at  a  time  will  come  in  contact  with  the  body,  and  in 
order  to  prevent  the  fibres  or  the  muscles  from   mutually 
supporting  each  other,  they  must  be  cut  one  at  a  time. 

For  these  reasons  the  edge  of  a  cutting  weapon  should 
be  curved,  and  the  blow  oblique  rather  than  direct. 

The  kind  of  curvature  of  the  edge  (convex  or  concave) 
will  depend  on  the  direction  in  which  the  weapon  is  moving 
at  the  time  of  the  blow.  If  moving  toward  the  object,  the 
edge  should  be  convex ;  if  from  it,  concave. 

Extreme  examples  are  seen  in  the  Turkish  sabre,  a,  and 
the  Arab  yataghan,  b,  Fig.  302. 

2.  In  order   to   give  force  to  the  blow,   the    centre  of 

528 


PORTABLE  ARMS.  $2$ 

gravity  should  be  well  forward  ;  an  example  is  seen  in  the 
axe. 

3.  For  facility  of  handling,  the  centre  of  gravity  shouM 
be  near  the  hilt. 


a 

FIG.  302. 

As  these  two  principles  are  conflicting,  a  compromise  is 
generally  effected  by  throwing  the  centre  of  gravity  well 
forward  in  a  cutting  weapon,  and  well  to  the  rear  in  a 
thrusting  one,  and  giving  it  an  intermediate  position  where, 
as  in  the  cavalry  sabre,  the  two  functions  are  combined. 

LIGHT  ARTILLERY  SABRE. — This  is  the  only  distinct  cut- 
ting weapon  in  service,  and  it  has  a  short  curved  blade  with 
a  comparatively  light  hilt  (Fig.  303),  the  centre  of  gravity 
being  well  forward.  The  cross-section  is  grooved  for 
lightness  and  strength. 


FIG.  303. 

305.  Thrusting  Arms— Principles— Straight  Sword— Bayonet — Lance 
—Cutting  and  Thrusting  Arms — Cavalry  Sabre. 

A  thrusting  arm  is  one  which  acts  by  its  point,  and  is 
based  upon  the  following  principles : 

1.  Its  penetration  depends  on  the  power  of  the  wedge  at 
its  point,  and  hence  this  point  or  wedge  should  be  as  sharp 
as  possible  consistent  with  strength. 

2.  For  a  given  power  of  wedge,  the  penetration  also  de- 
pends on  the  position  of  the  axis  of  the  wedge  with  reference 
to  the  thrusting  force.     Hence  the  blade   of   a  thrusting 


530  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

weapon  should  be  straight,  to  prevent  the  turning  aside  of 
the  point  by  the  oblique  component  of  this  force. 

3.   For  facility  of  handling,  the  centre   of  gravity  should 
be  well  to  the  rear,  and  the  blade  should  be  light. 
The  principal  thrusting  weapons  are 
The  straight  sword  ; 
The  bayonet ; 
The  lance  or  pike. 

THE  STRAIGHT  SWORD  (Fig.  304),  as  its  name  indicates, 
has  a  straight  blade  and  sharp  point,  and  the  centre  of  grav- 
ity well  to  the  rear  in  accordance  with  these  principles. 


o 


FIG    304. 


THE  BAYONET. — This  is  intended  to  convert  the  gun  into 
a  pike.  It  was  formerly  employed  very  extensively,  but  its 
use  has  gradually  decreased  as  ranges  and  velocities  have 
increased.  It  is  still  supplied  with  the  latest  model  guns, 
;and  is  shown  in  Fig.  305. 


FIG.  305. 


It  is  fixed  to  the  muzzle  of  the  gun  by  a  spring  clasp,  a, 
engaging  over  a  stud  on  the  upper  band,  and  by  a  ring,  b, 
which  encircles  the  muzzle. 


a 


,~~c 
-b 


FIG.  306. 


The  older  form  of  bayonet  in  use  on  the  Springfield 
Rifle  cal.  .45  is  shown  in  Fig.  306.  Its  cross-section  is 
shown  in  the  figure,  and  is  such  as  to  give  lightness  and 
stiffness. 


SMALL   ARMS.  53! 

The  parts  are  :  the  blade  a,  neck  or  shank  b,  socket  c, 
clasp  dy  and  groove  e.  Its  method  of  attachment  to  the  gun 
is  well  known. 

THE  LANCE  OR  PIKE. — This  is  still  used  in  some  foreign 
services,  and  is  a  sharp  steel  blade  fixed  to  the  end  of  a  long 
wood  handle.  This  handle  is  provided  with  a  loop  at  the 
centre  of  gravity,  for  convenience  in  carrying  and  guiding. 
It  has  the  advantage  of  greater  length  than  the  other  thrust- 
ing weapons,  but  is  inconvenient  to  carry  and  handle. 

CUTTING  AND  THRUSTING  ARMS — CAVALRY  SABRE.— 
These  weapons  combine  the  functions  of  the  other  two  classes 
and  hence  exhibit  features  common  to  each  class. 

THE  CAVALRY  SABRE  (Fig.  307)  is  the  only  weapon  of  this 


FIG.  307. 

class  in  service,  and  the  following  points  may  be  noted.  As 
it  is  used  both  for  cutting  and  thrusting,  its  blade  is  longer 
and  less  curved  than  that  of  the  light  artillery  sabre  ;  the 
hilt  is  heavier,  to  bring  the  centre  of  gravity  further  to  the 
rear,  and  the  hand  is  better  protected  by  the  guard. 

SMALL  ARMS, 

306.  Principal  Parts— The  Barrel— Calibre— Recoil. 

PRINCIPAL  PARTS. — The  essential  parts  of  all  breech-load- 
ing small  arms  are : 

The  barrel ; 

The  receiver  ; 

The  breech  mechanism  ; 

The  firing  mechanism ; 

The  sights  ; 

The  stock  and  mountings  ; 
and  for  magazine  arms 

The  repeating  mechanism. 


532  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

THE  BARREL — CALIBRE. — The  determination  of  the  cali- 
bre of  a  small  arm  involves  the  consideration  of  recoil,  initial 
velocity,  and  various  other  questions  which  will  be  discussed 
in  detail. 

RECOIL. — Experience  has  shown  that  a  certain  amount  of 
recoil  can  be  borne  by  the  soldier  without  fatigue.  The 
fatigue  caused  by  recoil  will  vary  not  only  with  the  weight 
of  the  arm  and  the  velocity  of  recoil,  but  also  with  the 
nature  of  the  powder,  the  inclination  of  the  small  of  the 
stock,  the  area  of  the  stock  resting  against  the  shoulder,  etc. 

For  convenience  of  carrying  and  to  avoid  fatigue  the 
weight  of  a  small  arm  should  not  greatly  exceed  9  Ibs.  This 
fixes  the  weight  of  the  barrel,  and  for  a  given  weight  of 
barrel,  or  of  gun,  we  conclude  generally  that  the  fatigue 
due  to  recoil  increases  with  the  velocity  of  recoil.  We  have 
for  the  velocity  of  recoil  while  the  projectile  is  in  the  bore, 
equation  (65),  Interior  Ballistics, 


>•=?(<+ 1). 


Since  P,  the  weight  of  the  gun,  is  fixed  by  other  con- 
siderations, as  above  explained,  the  velocity  of  recoil  can  be 
reduced  only  by  decreasing  the  initial  velocity  v  or  the 
weight  of  the  bullet/. 

Objections  to  Decreasing  Initial  Velocity.  —  These  are 
obvious.  The  object  of  all  improvements  in  modern  guns 
is  to  obtain  as  great  an  initial  velocity  as  possible,  keeping 
the  maximum  pressure  within  safe  limits,  as  this  increase  of 
velocity  gives  greater  energy,  longer  ranges,  flatter  trajec- 
tories, etc.,  as  will  be  explained.  It  is  evident,  therefore, 
that  the  fatigue  due  to  recoil  can  only  be  reduced  and  kept 
within  proper  limits  by  decreasing  the  weight  of  the  bullet. 

Advantages  of  Decreasing  Weight  of  Bullet. — Considering 
the  equation 


it  is  evident  that  for  an  allowable  value  of  v' ,  since  P  is 


SMALL   ARMS.  533 

constant,  a  decrease  in  the  weight  of  the  bullet  /,  will  in- 
crease the  initial  velocity  v. 

Therefore  a  decrease  in  weight  of  bullet  gives  a  value 
for  the  recoil  which  can  be  easily  supported  by  the  soldier, 
and  it  also  increases  the  initial  velocity  of  the  projectile, 
which  is  the  object  sought.  Whether  this  increase  in  initial 
velocity  will  be  advantageous  at  different  ranges  depends 
on  the  manner  in  which  the  weight  is  reduced,  and  it  is 
necessary  therefore  to  consider  the  best  method  of  doing 
this. 

307.  Reduction  of  Weight  of  Bullet  —  First  Method—  Decreasing  the 
Length,  keeping  the  Diameter  Constant. 

The  weight  of  the  bullet  may  be  decreased  : 

1.  By  decreasing  its  length,  keeping  the  diameter  con- 
stant. 

2.  By  decreasing  the  diameter,  keeping  the  length  con- 
stant. 

3.  By  changing  both  length  and  diameter. 

To  determine  which  of  these  methods  is  best,  assume  the 
equations 

dv        P 

dt=W'      ........     (438) 

Cdv 
v  =  d*  ........     (439) 


(440) 


v* 

—  =gcos  0.    .......     (441) 

Equations  (438)  and  (439)  are  from  Mechanics.  In  (438) 
P  is  the  total  pressure  acting  to  produce  acceleration,  and 
M  the  mass  of  the  projectile.  In  (439)  v  is  the  velocity  of 
the  projectile  at  any  time  /,  and  in  the  present  case  is  the 
initial  velocity.  Equations  (440)  and  (441)  are  from  Exterior 
Ballistics.  In  (440;  R  is  the  retardation  of  the  projectile 
due  to  the  resistance  of  the  air,  and  the  quantities  in  the 
second  member  are  all  defined  in  Exterior  Ballistics,  d  and 


534  TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY, 

W  being  the  diameter  and  weight  of  the  projectile.  In 
(441)  v  is  the  velocity  of  the  projectile  at  any  point  of  its 
trajectory,  P  the  radius  of  curvature  at  that  point,  and  0 
the  inclination  of  the  tangent,  g  being  32.2  ft.-seconds. 

DECREASING  LENGTH  OF  PROJECTILE,  DIAMETER  CON- 
STANT.— In  equation  (438), 

dv___P_ 
dt   ~  M' 

the  total  pressure  P  =  p'  X  i^2,  p'  being  the  pressure  of 
the  powder  per  unit  of  area  of  base  of  projectile. 

For  constant  values  of/'  and  d,  P  will  remain  constant. 
Hence  if  the  length  of  the  projectile  be  decreased,  the 
diameter  being  constant,  Mwill  decrease,  and  from  equation 

(438)  i-,  or  the  acceleration,  will  increase. 
In  equation  (439), 

*<fc 


=    fi 


dv 
since  —  increases,  v,  or  the  initial  velocity,  will  increase. 

In  equation  (440), 


since  ^decreases  while  ^remains  constant,  R  will  increase. 
This  will  cause  z>  to  decrease  for  all  points  of  the  trajec- 
tory, and  hence  in  equation  (441), 

ft  ~^C 

p  will  decrease,  or  the  trajectory  will  be  more  curved. 

If  /,  the  pressure   of  the  powder  per  square  inch,  be 
increased,  P  in  equation  (438)  will  increase,  and  hence  also 
dv 
•£.     This,  in  equation  (439),  will  cause  an  increase  in  v,  but 

since  from  (440)  the  retardation  is  still  great,  the  velocity 


SMALL   ARMS.     ,  535 

will  fall  oft  rapidly,  arid  from  (441)  the  trajectory  will  be 
very  much  curved. 

The  results  obtained  by  decrease  of  weight  of  bullet,  by 
the  method  of  shortening  it,  and  keeping  the  diameter  con- 
stant, are,  therefore  : 

1.  The  velocity  of  recoil  is  decreased; 

2.  The  initial  velocity  is  increased  ; 

3.  The  remaining  velocity  at  different  points  falls  off  very 
rapidly  ; 

4.  The  curvature  of  the  trajectory  is  increased. 

From  the  3d  and  4th  results  we  conclude  that  this 
method  of  reducing  the  weight  of  the  bullet  should  not  be 
adopted. 

308.  Reduction  of  Weight  of  Bullet—  Second  Method  —  Decreasing 
Diameter,  keeping  Length  Constant. 

In  equation  (438), 

dv__    P^ 
dt  ~~M> 

we  have  as  before 


Suppose/'  fixed  and  ^  decreased.  Then,  since  the  area 
of  cross-section  of  the  projectile  decreases  in  this  case,  P 
will  decrease  directly  with  it,  and  the  mass  M  will  also 
decrease  directly  with  the  same  area,  the  length  being  con- 

p 
stant,  and  hence  the  ratio  -jr=  will  not  change.     The  same 

may  be  shown  for  an  increase  in  diameter,  the  length  being 

constant. 

W 
The  sectional  density  of  a  projectile  is  --^  (see  Projec- 

tiles, subject  164).     Substituting  for  IV  its  value,  we  have 


W 

—    */  1 

'  ' 

or   the   sectional   density  varies  with   the   length.     Hence 
when  the  length  is  constant,  the    sectional  density  is  con- 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

stant,  and  from  the  above  we  conclude  that  for  the  same 
pressure  per  square  inch,  and  the  same  sectional  density  of 
projectile,  no  increase  of  velocity  is  obtained  by  reducing 
the  weight,  assuming  the  same  pressure  curve  in  the  two 
cases. 

In  equation  (440), 


since  T^and  v  do  not  change,  there  is  no  change  in  retarda- 

tion, and  consequently  there  is  no  change  in  curvature, 
equation  (441). 

Therefore  the  only  effect  of  reducing  the  weight  of  the 
projectile  by  decreasing  the  diameter  and  keeping  the 
length  constant,  or,  in  other  words,  keeping  the  sectional 
density  constant,  when  the  pressure  per  square  inch  p'  re- 
mains constant,  is  to  diminish  the  velocity  of  recoil. 

Suppose,  however,  that/'  is  increased. 

Then  in  equation  (438), 


M,  as  before,  will  decrease  directly  with  the  area  of  cross- 

p 
section,  but  P  will  increase,  and    hence  the    ratio  -^  will 

increase.     This  will  cause  -=-  to  increase. 

at 

In  equation  (439), 


v  will  increase.     In  equation  (440), 


R  remains  constant,  since  ^  does  not  change  ;  or  it  may 
even  decrease,  owing  to  the  increase  in  v,  and  the  conse- 


SMALL   ARMS.  537 

quent  change  in  the  exponent  of  f(v)  from  3  to  2  (see 
Mayevski's  experiments,  Exterior  Ballistics),  v  therefore 
will  be  greater  for  all  points  of  the  trajectory,  and  in 
equation  (441), 


g  cos  &    • 

p  will  be  greater,  and  hence  the  curvature  of  the  trajectory 
will  be  less,  or  it  will  be  flatter. 

Hence  by  decreasing  the  weight  of  the  bullet  by  the 
second  method,  that  is,  by  reducing  the  diameter  and  keep- 
ing the  length  constant,  and  at  the  same  time  increasing  the 
pressure  per  square  inch  of  the  powder-gas,  we  obtain : 

1.  A  decrease  in  velocity  of  recoil ; 

2.  An  increase  in  initial  velocity  ; 

3.  No  increase  in  retardation,  and  perhaps  a  reduction  ; 

4.  A  flatter  trajectory. 

309.  Reduction  of  Weight  of  Bullet— Third  Method — Changing 
Length  and  Diameter — Smokeless  Powder — Advantages  of 
Reduction  of  Calibre — Flatness  of  Trajectory. 

The  method  at  present  adopted  is  to  vary  the  pressure 
per  square  inch,  the  length,  diameter,  and  weight  of  projec- 
tile, so  as  to  obtain  the  best  ballistic  results.  This  has  led 
to  a  reduction  of  the  calibre  from  0.45  to  0.30  inch,  a  de- 
crease in  the  weight  of  the  bullet  from  500  to  220  grains, 
the  length  being  very  slightly  changed,  and  an  increase  of 
pressure  per  square  inch  from  a  maximum  of  30,000  Ibs.  to 
a  maximum  of  45,000  Ibs.  per  square  inch,  an  increase  of 
initial  velocity  from  1300  to  2000  ft.-seconds,  with  a  reduc- 
tion of  velocity  of  recoil  from  14  to  9.6  ft.-seconds,  and  of 
energy  of  recoil  from  27  to  1 1  foot-pounds. 

SMOKELESS  POWDER. — It  is  evident  that  to  obtain  any  bal- 
listic advantage  from  a  reduction  of  calibre,  the  pressure  per 
square  inch  on  the  projectile  must  be  increased.  When  the 
calibre  of  small  arms  was  first  reduced,  various  attempts 
were  made  to  obtain  this  increase  of  pressure  by  the  use  of 
the  old  black  powder  in  various  forms,  such  as  larger  charges 
compressed,  slower  burning,  etc.,  but  the  results  were  un- 


538  TEXT- BOOK  OF  ORDNANCE  AND    GUNNERY. 

favorable,  giving  high  and  irregular  pressures,  increase  of 
fouling,  etc.  The  effort  to  overcome  these  difficulties  led 
to  the  introduction  of  smokeless  powder.  Its  advantages 
have  been  explained  in  High  Explosives,  one  advantage  of 
great  importance  being  that,  as  the  smokeless  powder  burns 
more  slowly  and  regularly,  it  acts  upon  the  projectile  like 
the  slow-burning  powders  already  described  in  large  guns, 
and  hence  for  a  given  initial  value  of  /'  we  obtain  a  greater 
initial  velocity  than  would  be  produced  by  the  same  initial 
value  of/'  with  the  old  black  powders. 

ADVANTAGES  OF  REDUCTION  OF  CALIBRE. — The  princi- 
pal of  these  are  : 

1.  Flatness  of  trajectory,  and  increase  of  range  ; 

2.  Decrease  in  weight  of  cartridges  ; 

3.  Increase  of  accuracy  of  fire  ; 

4.  Decrease  of  recoil  ; 

5.  Increased  penetration. 

FLATNESS  OF  TRAJECTORY. — The  advantage  of  this  may 
be  illustrated  as  follows :     Assume,  equation  (441), 


g  cos  6' 


Let  Hj  Fig.  308,  be  the  height  of  a  man,  and  suppose 
this  height  to  be  the  maximum  height  of  the  trajectory. 
The  total  range  in  this  case  is  called  the  maximum  contin- 
uous dangerous  space,  and  is  frequently  used  in  comparing 
the  ballistic  qualities  of  guns. 

The  value  of  cos  0  =  i  at  the  summit  of  the  trajectory; 
hence 


for  this  point     It  is  evident  that  p  increases  rapidly  with  v. 

Hence  for  a  low  velocity  we  will  have   the   trajectory 

AB,  and  for  a  high  velocity,  A'B',  the  maximum  continuous 


SMALL   ARMS.  539 

dangerous  spaces  beinsr  the  horizontal  distances  AB  and  A' B' 
respectively.  The  flat  trajectory,  then,  gives  a  greater  con- 
tinuous dangerous  space  A'B',  and  this  is  true  when  the 
dangerous  space  is  not  continuous,  as  in  the  case  of  the  ob- 
ject H'\  the  dangerous  spaces  being  H'B  and  BB'  respect- 
ively. 

An  error  in  estimating  distance  is  also  of  less  importance 
with  a  flat  trajectory ;  as  in  the  figure,  an  error  H'B  for  the 
curved  trajectory,  and  BB'  for  the  flat  one,  may  be  com- 
mitted, and  the  target  will  still  be  struck.  The  distances 
AB  and  A' B'  for  the  calibres  .45  and  .30  are  418  and  600 
yards  respectively. 

310.  Advantages  of  Reduction  of  Calibre — Decrease  in  Weight  of 
Cartridges — Increase  of  Accuracy  of  Fire — Increased  Pene- 
tration. 

DECREASE  IN  WEIGHT. — The  number  of  rounds  carried 
is  limited  by  the  physical  endurance  of  the  soldier,  just  as 
the  weight  and  recoil  of  his  piece  are  fixed  by  the  same 
conditions.  A  reduction  in  the  weight  of  the  cartridge  in- 
creases the  number  of  rounds  that  can  be  carried,  and  this 
increase  is  very  important  owing  to  the  great  increase  in 
rapidity  of  fire  with  modern  breech-loaders,  and  the  dif- 
ficulty of  supplying  the  fighting-line  writh  fresh  ammunition. 
This  reduction  in  weight  is  due  not  only  to  the  reduction 
in  calibre,  but  also  to  the  introduction  of  smokeless  powder, 
by  which  the  weight  of  the  charge  has  been  reduced  nearly 
one  half. 

INCREASE  OF  ACCURACY  OF  FIRE. — Owing  to  the  greater 
velocities  at  all  points  of  the  trajectory,  the  small-calibre  pro- 
jectile is  less  affected  by  the  wind  and  other  deviating  causes, 
and  the  drift  is  not  greater  than  with  the  old  projectile. 
Hence  the  horizontal  deviations  are  less  than  with  the  old 
projectile.  As  has  already  been  shown,  the  flatness  of  trajec- 
tory makes  it  more  accurate  in  a  vertical  direction,  and  hence 
its  absolute  accuracy,  which  is  taken  to  be  the  radius  of  the 
circle  containing  one  half  the  whole  number  of  shots,  is 
greater  than  with  the  old  bullet,  the  radius  of  the  circle 
being  less. 


54°  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

There  is,  however,  one  exception  to  this.  Owing  to  the 
relative  increase  in  length  of  the  new  bullet,  it  is  necessary 
to  give  it  greater  velocity  of  rotation  about  its  longer  axis 
to  insure  stability,  and  hence  the  pitch  of  the  rifling  is  more 
rapid  for  the  new  small  calibre. 

This  increases  the  passive  resistances  in  the  bore,  and, 
with  the  greater  pressure  per  square  inch  on  the  projectile, 
causes  increased  vibration  of  the  barrel.  The  result  is  that 
for  short  ranges  the  accuracy  of  the  small  calibre  is  slightly 
less  than  that  of  the  old  arm. 

Beyond  these  ranges  the  small  calibre  is  more  accurate. 

INCREASED  PENETRATION. —  This  is  due  to  increase  of 
velocity,  and  also  to  the  fact  that  the  exterior  of  the  bullet 
is  covered  with  a  jacket  of  harder  metal,  such  as  copper, 
German  silver,  or  nickeled  steel.  This  jacket  holds  the 
projectile  together  and  prevents  deformation  on  striking. 
It  is  stated  that  the  bullet  of  the  8-mm.  rifle  has  pierced  a 
tree  17  inches  in  diameter,  and  afterwards  passed  through 
the  bodies  of  five  men.  The  penetration  of  the  cal.  .30  bullet 
with  steel  jacket  is  in  sand  14  inches,  and  in  oak  from  16 
to  24  inches,  the  target  being  3  ft.  from  the  muzzle.  The 
penetration  of  the  cal.  .45  bullet  under  the  same  circum- 
stances is  3.3  inches  in  oak. 

Numerous  experiments  have  been  made  upon  human 
bodies  to  test  the  effect  of  the  small-calibre  bullet,  with  the 
general  result  that  the  wounds  are  less  serious  and  the  shat- 
tering effect  on  the  bones  less  than  with  the  old  projectile. 
The  shock  or  stopping  power  is  also  less  as  the  calibre 
decreases,  unless  the  bullet  acts  explosively,  and  hence  it  has 
been  proposed  for  the  very  small  calibres  to  remove  the 
jacket  from  the  point  of  the  bullet,  thus  causing  it  to  spread 
out  in  front  on  striking. 

311.  Disadvantages  of  Reducing  the  Calibre. 

The  principal  of  these  are: 

i.  The  decrease  in  weight  of  bullet,  and  hence  the  rela- 
tive increase  in  its  length,  necessitates  a  more  rapid  twist  of 
rifling  to  give  it  stability  in  flight,  and  this  increase  of  twist 
increases  the  passive  resistances  in  the  bore  and  gives  rise 


SMALL   ARMS.  541 

to  greater  vibrations  of  the  barrel.  These  vibrations,  as 
stated,  decrease  the  accuracy  for  short  ranges.  A  test  with 
the  barrel  confined  in  a  fixed  rest  showed  greater  inaccuracy 
at  500  yards  than  with  the  cal.  .45.  A  heavy  barrel  cal.  .30, 
made  expressly  for  the  purpose,  was  then  tried  in  the  fixed 
rest  under  similar  conditions,  and  remarkable  accuracy, 
greater  than  ever  before  recorded,  was  obtained.  This 
shows  that  the  inaccuracy  is  due  to  vibrations  of  the  barrel, 
and  it  is  probable  that  when  the  gun  is  fired  from  the 
shoulder  in  the  ordinary  manner  the  targets  will  be  much 
better  than  when  a  fixed  rest  is  used,  as  the  barrel  in  this 
case  will  not  be  rigidly  held,  and  consequently  its  vibrations 
will  be  less. 

The  increase  in  twist  also  renders  the  projectile  more  apt 
to  strip  in  the  bore;  that  is,  to  be  forced  across  the  lands 
without  taking  the  rifled  motion,  with  the  result  that  the 
bore  is  scored  or  fouled  by  the  metal,  and  the  projectile 
rotates  about  its  shorter  axis  in  flight,  or  tumbles.  This 
has  been  remedied  by  the  use  of  a  harder  metal  jacket. 

2.  The  cleaning  of  the  bore  is  more  difficult.     Since  the 
introduction  of  smokeless   powder  this   objection   has   less 
weight. 

3.  The  manufacture  is  more  difficult. 

This  has  been  a  serious  objection,  as  it  is  a  very  difficult 
operation  to  bore  and  rifle  accurately  such  a  small  calibre, 
and  any  inaccuracy  here  is  fatal  to  the  accuracy  of  fire. 
This  difficulty  has  also  been  overcome,  and  guns  below  0.30 
calibre  are  now  successfully  made. 

4.  The  pressure  in  the  bore  is  greater. 

The  necessity  for  this  has  been  shown,  and  it  has  been 
difficult  to  provide  steel  of  sufficiently  high  elastic  qualities 
to  withstand  this  pressure.  It  has  also  caused  the  abandon- 
ment of  nearly  all  the  old  forms  of  breech  mechanism,  in 
order  to  obtain  a  secure  fermeture. 

In  spite  of  these  objections,  the  great  advantages  of  a 
reduction  of  calibre  have  led  to  its  universal  adoption  in  all 
countries,  and  the  tendency  now  is  to  go  below  the  .30 
calibre.  This  has  been  done  in  some  countries.  One  of 
the  points  still  in  doubt  is  the  effect  of  the  small-calibre 


542  TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 

bullet  upon  the  nervous  system,  and  whether  a  wound  from 
this  bullet,  when  not  fatal,  will  stop  a  man. 

This  can  only  be  solved  in  actual  war,  and  hence  in  our 
service  it  has  been  thought  best  not  to  go  below  the  cal.  .30 
at  present. 

312.    Rifling— Pitch — Number  of   Grooves    and    Lands — Width — 
Depth— Direction  of  Twist. 

PITCH. — The  pitch  of  the  rifling  in  small  arms  is  alwrays 
uniform,  because,  when  fired,  the  bullet  is  molded  accurately 
into  the  grooves  and  lands,  and  the  length  of  the  surface  of 
the  bullet  in  contact  with  the  bore  is  great.  If  the  pitch  be 
uniform,  no  change  of  form  of  the  molded  surfaces  takes 
place  during  the  passage  of  the  projectile  from  breech  to 
muzzle ;  if  the  pitch  be  increasing,  a  change  of  form  is  con- 
stantly occurring,  resulting  in  increased  resistance,  deform- 
ation of  projectile,  and  inaccuracy. 

It  has  been  found  necessary  in  practice  to  increase  the 
twist  as  the  calibre  decreases,  as  already  explained  (see  sub- 
ject 163). 

In  the  Springfield  cal.  .45  the  twist  is  one  turn  in  48.9 
calibres,  in  the  new  cal.  .30  it  is  one  turn  in  33^  calibres,  or 
one  turn  in  22  and  10  inches  respectively. 

NUMBER  OF  GROOVES  AND  LANDS. — The  number  of 
grooves  has  no  effect  apparently  upon  the  accuracy  of  fire,  and 
hence  for  convenience  of  manufacture,  cleaning,  and  strength, 
these  are  as  few  as  possible.  The  cal.  .45  has  three  grooves 
and  lands,  the  cal.  .30  four.  As  a  general  rule  the  number 
has  varied  from  three  to  seven. 

WIDTH  OF  GROOVES  AND  LANDS.— The  width  depends  on 
the  kind  of  bullet.  When  of  hardened  lead,  the  bullet  is 
slightly  upset  by  the  shock  of  discharge  and  forced  into  the 
grooves,  the  lands  cutting  into  the  projectile.  As  this  metal 
offers  comparatively  little  resistance,  and  the  twist  is  not 
rapid,  the  grooves  and  lands  in  the  cal.  .45  are  of  equal  width. 

With  the  jacketed  bullet,  the  resistance  to  'deformation 
being  much  greater,  the  grooves  are  wider  and  the  lands 
narrower,  since  these  latter  do  the  work  of  cutting  into  the 


SMALL    ARMS. 


543 


projectile.  In  the  U.  S.  cal.  .30  the  grooves  are  three  times 
the  width  of  the  lands. 

DEPTH  OF  GROOVES  AND  LANDS. — If  the  depth  of  groove 
is  too  great,  there  is  too  much  work  lost  in  forcing  the  projec- 
tile, and  the  forcing  may  not  be  perfectly  accomplished. 
This  latter  will  cause  erosion  and  inaccuracy.  If  the  depth 
is  too  small,  the  groove  may  be  easily  filled  by  fouling.  The 
depth  also  varies  with  the  kind  of  bullet.  The  depth  of 
groove  in  the  Springfield  cal.  .45  is  .005  inch,  and  in  the 
cal.  .30  it  is  .004  inch. 

The  exterior  diameter  of  the  lead  bullet  is  0.457  inch, 
that  of  bore  at  bottom  of  grooves  .455  inch  (see  Fig.  309). 

Hence  with  the  Springfield  rifle,  in  addition  to  the  work 
done  by  the  lands  in  cutting  into  the  projectile,  the  latter 
-exceeds  the  diameter  of  the  bore  at  bottom  of  grooves  by 
.002  inch.  This,  added  to  the  upsetting  action  of  the  pow- 
der, gives  a  very  energetic  forcing,  and  insures  its  accom- 
plishment, but  without  great  strain  on  the  gun.  The 
cannelures  or  grooves  in  the  bullet  also  assist  in  reducing 
the  work.  With  the  cal.  .30  the  exterior  diameter  of  the 
bullet  is  0.308  inch,  and  that  of  the  bore  at  the  bottom  of 
grooves  the  same.  Hence  the  bullet  exactly  fills  the  bore 
from  groove  to  groove,  and  there  is  no  forcing  in  the 
grooves,  aside  from  what  may  be  due  to  upsetting  of  the 
metal  by  the  action  of  the  powder  and  the  pressure  of  the 
lands. 


FIG.  309. 


FIG.  310. 


In  general  the  grooves  have  the  same  depth  from  breech 
to  muzzle.  In  the  case  of  the  Martini-Henry  rifle  recently 
used  in  the  English  service,  the  depth  of  groove  decreased 


1II7B- 


544  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

from  breech  to  muzzle,  to  make  the  forcing  more  gradual, 
and  thus  decrease  the  pressure  at  the  origin,  ana  conse- 
quently the  vibrations. 

Figs.  309  and  310  show  the  cal.  .45  and  cal.  .30  grooves 
in  section. 

DIRECTION  OF  TWIST. — This  has  no  influence  upon  the 
accuracy  of  fire,  as  it  produces  "  drift,"  which  can  be  allowed 
for.  All  small  arms  are  rifled  with  a  right-hand  twist,  and 
the  resulting  drift  is  to  the  right  as  already  explained. 

A  case  occurs  in  the  French  service,  where  the  vibrations 
of  the  barrel,  owing  to  the  peculiarity  of  the  breech  mech- 
anism, caused  the  bullet  to  deviate  to  the  right,  and  to 
correct  this  the  gun  was  rifled  with  a  left-hand  twist. 

313.  Profile  of  Chamber— Thickness  and  Length  of  Barrel. 


FIG.  311. 

PROFILE  OF  CHAMBER. — The  chamber  is  made  slightly 
conical  to  facilitate  the  extraction  of  the  cartridge-case. 
That  for  the  cal.  .30  rifle  is  shown  in  Fig.  311.  The  chamber 
must  be  free  from  all  cuts  or  scratches,  since  the  cartridge- 
case  will  be  forced  into  them  on  firing,  and  will  either  stick 
or  rupture.  All  dimensions  must  be  exact,  and  very  little 
variation  can  be  allowed. 

THICKNESS  OF  BARREL.— The  case  is  that  of  a  single 
cylinder  under  extension,  the  exterior  pressure  being  zero 
(see  "  Elastic  Strength  of  Guns  ").  For  the  thickness  of  the 
cal.  .30  rifle-barrel  just  in  front  of  the  powder-chamber, 
assume,  equation  (205), 


SMALL   ARMS.  545 

We  have 

r,  .30 

-#o  =  —  =  ^S* 

Bo  =  61,500  Ibs., 
P00  =  40,000  Ibs., 

which  values  substituted  in  the  above  equation  give 
Rl  —  R0  =  .3429  inch  =  1.14  calibres. 

The  actual  thickness  is  0.34  inch  =  0.49  —  0.15  =  0.34. 

For  the  thickness  at  various  points  along  the  bore  the 
pressure  curve  must  first  be  calculated,  but  other  considera- 
tions, such  as  stiffness  to  resist  vibrations  and  to  prevent 
bending  in  service,  etc.,  enter,  and  the  exterior  is  given  the 
general  form  of  a  conical  frustum,  the  thickness  at  the 
muzzle  being  0.53  calibres,  0.16  inch. 

LENGTH  OF  BARREL.— This  is  so  adjusted  that  the  rear- 
rank  man  can  fire  over  the  shoulder  of  the  man  in  front 
without  danger  to  the  latter,  and  for  the  small-calibre  rifle 
this  length  is  fixed  at  30  inches  (100  calibres). 

Experiment  shows  that  increasing  this  length  gives  very 
little  increase  of  initial  velocity,  while  it  increases  weight 
and  difficulty  of  manufacture.  The  length  of  the  cal.  .45 
barrel  is  32.6  inches.  The  length  of  travel  of  the  projectile 
in  the  bore  for  the  cal.  .30  is  28.19  inches  (94  calibres),  and 
for  the  cal.  .45,  30.445  inches  (67.6  calibres). 

314.  The    Receiver— General  Features — Receiver    for    Springfield 
Rifle. 

THE  RECEIVER  is  a  distinctive  feature  of  breech-loading 
small  arms,  and  forms  an  extension  of  the  barrel,  for  the 
purpose  of  receiving  the  cartridges  and  breech  mechanism. 

GENERAL  FEATURES. — The  shape  of  the  receiver  depends 
on  the  breech  mechanism,  and  also  upon  whether  the  gun 
is  a  single-loader  or  a  magazine  arm. 

In  general  it  must  have  the  following  features: 

1.  A  method  of  attachment  to  the  barrel. 

2.  A  method  of  attachment  to  the  stock. 


546 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


3.  An  opening  through  which   cartridges  are  inserted, 
empty  shells  extracted,  and  in  which   the   breech-block   or 
bolt  works. 

4.  An   axis   about  which  the  block    rotates,   or  guide- 
grooves  for  regulating  the  motion  of  the  bolt. 

5.  A  recess  or  groove  for  locking  the  block  or  bolt. 

6.  An  arrangement  for  ejecting  empty  cartridge-shells ; 
and  for  a  magazine  arm  in  addition  to  the  above— 

7.  An  opening  for  the  admission  of  cartridges  from  the 
magazine. 

8.  A  "  cut-off "  by  which  this  opening  may  be  used  or 
not  at  will. 

RECEIVER  FOR  SPRINGFIELD  RIFLE.— Fig.  312  shows  the 
receiver  for  the  Springfield  rifle. 


FIG.  312. 


It  is  attached  to  the  barrel  B  by  the  screw-threads  a ;  to 
the  stock,  by  a  screw,  b,  passing  through  the  tang  c\  d  is 
the  opening  through  which  the  cartridges  are  fed,  and  in 
which  the  breech-block  works ;  //  is  the  axis  about  which 
the  breech-block  rotates;  g,  the  recess  into  which  the  breech- 
block is  locked  by  its  cam-latch,  to  be  described ;  /  is  the 
ejector  spring  and  spindle.  The  cartridge-case  is  loosened 
in  its  seat  by  the  positive  action  of  the  extractor  E,  which 
rotates  in  the  direction  of  the  arrow.  The  axis  of  the 
spindle  of  the  spring  /is  at  first  above  the  axis  of  rotation, 
H,  of  the  block  and  extractor.  After  a  small  rotation  of  E, 
the  axis  of  the  spindle  is  carried  below  the  axis  H,  and  the 
spring  /  then  acts  to  rotate  E  quickly,  and  throw  out  or 
eject  the  empty  case.  As  the  case  moves  backward,  it 
strikes  the  inclined  stud  /,  and  is,  by  it,  deflected  upward 
out  of  the  receiver. 


SMALL   ARMS.  547 

-315.  Receiver  for  Cal.  .30. 

This  is  shown  in  Fig.  313. 

It  is  attached  to  the  barrel  by  a  screw-thread,  and  to  the 
stock  by  the  sere  ws  Jf  and  Fpassing  through  the  trigger-guard 


FIG.  313. 

into  it  from  below  (see  Fig.  336) ;  z  is  the  opening  through 
which  the  cartridges  are  fed  when  the  gun  is  used  as  a 
single-loader,  and  z'  when  used  as  a  magazine  arm.  The 
left  side,  r,  of  the  opening  z,  is  parallel  to  the  axis  of  the 
bore  and,  together  with  the  surface,  r* ',  on  the  right,  forms 
a  guide  for  the  bolt  when  moving  forward  or  back.  A 
second  groove,  h,  forms  a  recess  for  the  operating-handle  of 
the  bolt  to  rest  in,  when  this  handle  is  rotated  to  the  right 
in  closing  the  breech.  The  forward  shoulder  or  cam,  s,  in 
front  of  the  groove,  kt  is  so  shaped  as  to  give  a  screwlike 
motion  to  the  bolt  in  closing,  thus  moving  it  slowly  forward 
to  its  seat  against  the  breech.  The  rear  shoulder,  /,  arrests 
the  forward  motion  of  the  bolt  in  closing.  A  third  groove, 
k,  prevents  the  firing  mechanism  from  turning  with  the  bolt 
in  closing  the  breech. 

The  groove  a  locks  the  bolt,  a  lug  on  the  latter  entering 
it.  When  in  the  firing  position,  the  pressure  of  the  gas  is 
transmitted  to  the  surface  of  the  groove  a ;  the  surface  s,  and 
the  rear  surface  of  the  groove  //,  acting  as  safety-supports. 

The  empty  shell  is  ejected  as  follows:  The  bolt  is  drawn 
slowly  backward  at  first,  by  the  action  of  the  inclined  sur- 
face, /,  of  the  groove  /*,  against  the  operating-handle.  The 
extractor,  which  is  on  the  bolt,  and  engaged  with  the  rim 
of  the  cartridge,  draws  the  case  back  slowly,  due  to  this 
motion  of  the  bolt.  When  the  bolt  is  free  to  move  along 


548  TEX 7 '-BOO K   OF  ORDNANCE   AND    GUNNERY. 

the  axis  of  the  receiver,  it  moves  quickly,  drawing  back  the 
empty  case. 

At  the  end  of  the  travel  of  the  bolt,  the  short  arm,  e,  of 
the  ejector-lever, 'in  the  bottom  of  the  receiver,  is  struck  by 
a  shoulder  at  the  end  of  a  groove  in  the  bolt,  and  the  long 
arm,y,  is  thrown  up,  striking  the  empty  case  and  ejecting 
it.  The  opening  m  is  the  magazine,  which  will  be  explained 
later. 

The  cut-off  for  the  magazine,  Fig.  314,  is  a  pin  or  rod, 
the  rear  part,  a,  of  which  is  round,  and  the  front  part,  r,  is 

cut  away  partly,  as  shown.  The 
cut-off  is  inserted  in  the  left-hand 
side  of  the  receiver,  parallel  to 
its  axis  (see  Fig.  313,  C),  the  cut- 
F  away  portion,  c,  projecting  over 

the  opening  z'  of  the  magazine. 
When  the  magazine  is  in  use,  the  flat  part  of  the  cut-off 
forms  a  portion  of  the  surface  z'  of  the  magazine  opening. 
When  the  rnagazine  is  to  be  cut  off,  the  rod  is  rotated  by 
turning  the  handle  C.  This  brings  the  rounded  part  of  c 
into  such  a  position  that  it  projects  into  the  opening  z'  and 
forces  the  cartridges  down  slightly,  so  that  the  bolt  will 
pass  over  without  touching  them. 

The  cut-off  is  held  in  the  open  or  closed  position  by  the 
spring  C',  which  works  in  a  groove  in  the  receiver. 

316.    Breech    Mechanism — General   Classification — Sliding    Mech- 
anism. 

The  functions  of  the  breech  mechanism  are  to  open,  close, 
and  lock  the  breech,  extract  the  empty  cartridge-case,  and 
for  magazine  arms,  in  addition,  to  operate  the  repeating 
mechanism,  and  insert  the  cartridge. 

GENERAL  CLASSIFICATION.— Breech  mechanisms  may  be 
classified  generally  into : 

1.  Those  which  operate  by  sliding. 

2.  Those  which  operate  by  rotation. 
SLIDING  MECHANISM.— The  sliding  may  take  plac 
i.  By  the  motion  of  the  barrel  parallel  to  its  axis. 


SMALL  ARMS.  549 

This  arrangement  is  now  obsolete,  and  is  unsuitable  for 
^a  military  weapon  on  account  of  the  weight  of  the  barrel. 

2.  By  the  motion  of  the  breech-block  parallel  to  its  axis. 
Guns  with  this  mechanism  are  called  bolt-guns,  and  the 

mechanism  resembles  in  its  action  the  bolt  of  a  door,  whence 
the  name.  All  magazine  arms  at  present  in  use  belong  to 
this  system.  It  presents  the  following  advantages : 

a.  Extreme  simplicity,  great  strength,  and  small  number 
of  parts. 

b.  Secure  locking  against  the  effects  of  discharge. 

c.  Ease  of  extraction  of  empty  case. 

d.  Better  adapted  to  magazine  arms  than  any  other  sys- 
tem. 

The  objections  to  the  system  formerly  were  : 

a.  Danger  of  blowing  out  the  bolt  by  premature  dis- 
charge, before  the  breech  was  securely  locked. 

b.  Liability  to  explode  the   cartridge  when  pushing  it 
home,  either  by  striking  it  a  blow,  or  by  the  projection  of 
the  firing-pin  striking  the  primer  in  the  cartridge-case. 

These  objections  have  been  overcome. 

3.  The  block  may  slide  at  right  angles  to  the  axis  of  the 
barrel.     An  example  in  seen  in  the  Krupp  fermeture. 

The  advantage  of  this  system  is  that  it  is  not  liable  to 
blow  out,  as  the  direction  of  the  pressure  is  normal  to  the 
bearing  surfaces  of  the  block  ;  the  disadvantages  are  that  it 
tends  to  guillotine  the  cartridge,  does  not  push  it  home,  and 
renders  extraction  of  the  empty  case  difficult. 

317.  Rotating  Mechanism. 

The  rotation  may  take  place — 

1.  Around  an  axis  parallel  to  the  axis  of  the  gun,  and  at 
one  side.     This  is  now  obsolete. 

2.  Around  an  axis  parallel  to  the  axis  of  the  gun,  and 
below  it;  example,  revolvers. 

This  system  is  objectionable  for  a  military  arm,,  on 
account  of  the  weight  of  the  revolving  cylinder,  and  also 
because  of  the  break  in  the  barrel  at  the  junction  of  the 
cylinder  and  barrel  proper,  through  which  gas  may 
escape. 


550 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY, 


3.  Around  an  axis  at  right  angles  to  the  axis  of  the  gun,, 
above  that  axis,  and  at  the  front  of  the  block ;  example,  the 
Springfield  rifle  cal.  .45. 

This  system  has  the  following  advantages: 

a.  The  block  acts  to  push  the  cartridge  home  in  clos- 
ing. 

b.  It  forms,  in  connection  with  the  extractor,  a  strong 
lever  for  extracting  the  empty  case. 

c.  It  is  simple  and  has  comparatively  few  parts. 
Its  disadvantages  are : 

a.  It  does  not  securely  and  positively  lock  the  block,  and 
the  tendency  of  the  pressure,  is  to  force  it  strongly  against 
the  breech-recess  ;  hence  for  high  pressures,  as  in  the  present 
small  calibre,  it  is  difficult  to  open  after  firing. 

b.  It  is  not  adapted  for  a  magazine  arm. 

4.  Around  an  axis  at  right  angles  to  the  axis  of  the  bore,, 
above   that   axis,  and   in  rear  of  the  block ;    example,   the 
Martini-Henry  recently  used  in  the   English    service  (Fig. 

315). 


\ 


FIG.  315. 


The  advantages  of  this  system  are: 

a.  It  is  simple  and  solid,  and  the  block  is  well  protected 
against  accident. 

b.  The  pressure  does  not  tend  to  blow  open  the  block. 
Its  disadvantages  are : 

a.  A  space  must  be  left  between  the  front  of  the  block 


SMALL   ARMS.  551 

and  the  rear  of  the  chamber  to  allow  for  rotation  of  the 
block,  and  hence  the  chamber  cannot  be  tightly  closed. 

b.  The  extraction  of  the  empty  case  is  difficult. 

c.  The  block  is  liable  to  guillotine  the  cartridge,  unless 
the   latter    is  forced   completely   home  before  closing   the 
breech. 

5.  Around  an  axis  at  right  angles  to  the  axis  of  the  gun, 
below  that  axis,  and  in  front  of  the  block;  example,  the 
Remington,  Fig.  316. 


FIG.  316. 

This  system  is  simple,  but  requires  an  exact  adjustment 
of  all  the  parts,  especially  of  the  hammer,  as  in  addition  to 
its  ordinary  functions  it  locks  the  breech-block. 

A  system  is  also  used  in  which  the  barrel  rotates  about 
an  axis  at  right  angles  to  the  bore  and  below  that  axis ; 
example,  shot-guns.  This  is  not  used  for  military  arms,  on 
account  of  the  weight  of  the  barrel. 

318.  Requirements  of  a  Good  Breech  Mechanism. 

A  good  breech  mechanism  should  fulfil  the  following 
requirements: 

1.  It  should  be  simple,  strong,  and  safe  in  action,  and 
should  work  freely  under  all  conditions  which  are  liable  to 
prevail  in  active  service,  even  when  rusty  or  covered  with 
dust. 

2.  It  should  be  easy  to  clean,  take  apart  and  assemble, 


552  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

and  should  be  composed  of  few  pieces,  which  are  not  liable 
to  break  or  work  loose,  and  which  are  interchangeable. 
Screws  are  objectionable,  as  they  are  liable  to  work  loose. 

3.  The  motions  in  loading  should  be  as  few  as  possible, 
and  executed  in  regular  order,  and  it  should  be  impossible 
to  fire  the  gun  till  the  breech  is  securely  locked. 

4.  To  increase  the  rapidity  of  fire,  the  motion  of  opening 
and  closing  the  breech  should  cock  the  firing  mechanism. 
In  general  it  is  preferable  to  cock  the  firing  mechanism  by 
the  motion  of  opening    the  breech,  as    this   withdraws   the 
firing-pin  so  that  it  will  not  strike  the  primer  of  the  cartridge 
when  the  latter  is  pushed  home,  and  in  addition,  if  the  mech- 
anism is  cocked  in  closing,  a  slip  of  the  hand  before  the  bolt 
is  home   will    cause  the   latter  to  spring  back,  and  either 
throw  out  the   cartridge  which  is  partly  introduced,  or,  in 
case  of  a  magazine  arm,  it  may  cause  the  introduction  of  a 
second  cartridge  before  the  mechanism,  and  thus  produce 
jamming. 

5.  The  opening  of  the  breech  should  automatically  eject 
the  empty  case. 

6.  The  working  of  the  mechanism  should  cause  as  little 
fatigue  as  possible  to  the  firer. 

7.  A  safety-device  should    be  provided   which   can   be 
readily  seen  and  operated,  and  by  which  the  mechanism  can 
be  locked  in  place  and  accidental  discharge  rendered  im- 
possible. 

8.  It  should  be  impossible  to  strike  a  blow  on  the  car- 
tridge, either  by  the  bolt,  or  by  the  firing-pin,  while  the 
breech  is  being  closed. 

319.  Breech  Mechanism  of  Springfield  Rifle,  Cal.  .45. 

This  mechanism  belongs  to  the  system  in  which  the 
block  rotates  about  an  axis  perpendicular  to  the  axis  of  the 
gun,  above  that  axis,  and  in  front  of  the  block. 

Although  it  is  to  be  replaced  by  the  cal.  .30,  the  arm  is  still 
(1895)  in  service,  and  is  likely  to  be  used  in  any  emergency 
arising  within  the  next  few  years,  and  hence  its  mechanism 
will  be  explained. 


SMALL   ARMS. 

The  principal  parts  are  (Fig.  317): 
The  breech-block  D\ 
The  hinge-pin  H  ; 
The  cam-latch  G ; 
The  extractor  E  ; 
The  ejector  spring  and  spindle  /. 


553 


FIG.  317. 

The  receiver  and  ejector  spring,  spindle,  and  stud  have 
been  previously  explained. 

THE  BREECH-BLOCK. — This  has  an  oblique  hole,/,  Fig. 
318,  through  it  for  the  firing-pin.  In  front  is  the  hinge-pin 
hole  h,  which  is  elongated  parallel  to  the  axis  of  the  bore, 
and  through  which  passes  the  hinge-pin  H,  Fig.  317,  around 


FIG.  318. 

which  the  block  rotates.  In  rear  is  a  recess,  k,  called  the 
cam-latch  recess,  for  the  cam-latch  G  and  its  spring  K,  Fig. 
317.  The  shaft  of  the  cam-latch  passes  through  the  hole^-'. 

THE  HINGE-PIN. — This  forms  the  axis  about  which  the 
block  rotates.  It  passes  through  two  holes  in  the  lugs  of 
the  receiver,  and  is  kept  from  turning  by  an  arm  with  a  stud 
which  fits  in  a  hole  on  the  side  of  the  receiver. 

THE  CAM-LATCH.— This  locks  the  breech-block  in  firing 
by  entering  a  circular  recess,  g,  in  the  breech-screw  C,  Fig. 
317.  It  is  fixed  to  a  shaft  one  end  of  which  passes  through 
the  hole^-',  Fig.  318,  in  the  block,  and  the  other  end  is  sup- 


554  TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 

ported  by  the  breech-block  cap  g",  which  is  removable. 
The  axis  of  the  cam-latch  shaft  projects  on  the  right-hand 
side,  and  to  it  is  attached  a  thumb-piece  by  which  the  cam- 
latch  is  operated.  This  axis  fits  loosely  in  the  hole  g1  in  the 
breech-block,  and  also  in  the  corresponding  hole  in  the 
breech-block  cap^-". 

The  cam-latch  is  pressed  to  the  rear  into  its  recess  in  the 
breech-screw  by  the  cam-latch  spring  K. 

THE  EXTRACTOR.  —  This  is  mounted  on  the  hinge-pin,  on 
the  left  side  of  the  chamber.  Part  of  its  lower  extremity  is 
cut  into  such  a  shape  as  to  form,  when  in  place,  a  part  of 
the  couriterbore  of  the  chamber,  in  which  the  rim  of  the 
cartridge  rests.  It  has  also  in  front,  and  slightly  above  the 
axis  of  the  hinge-pin,  a  recess  for  the  reception  of  the  head 
of  the  ejector-spindle;  and  a  lug,  e,  Fig.  317,  projects  be- 
yond the  upper  surface  of  the  receiver,  against  which  the 
breech-block  bears  in  opening. 

ACTION  OF  MECHANISM.  —  When  the  piece  is  fired,  the 
breech-block  slides  bodily  to  the  rear,  owing  to  the  elonga- 
tion of  the  hinge-pin  hole  k,  Fig.  318.  Owing  to  this  motion 
of  the  block,  and  to  the  loose  fit  of  the  cam-latch  shaft  in  its 
holes  in  the  block,  the  pressure  of  the  powder-gas  is  trans- 
mitted directly,  through  the  breech-block  and  the  body  of 
the  cam-latch,  to  the  breech-screw  C,  and  there  is  no  strain 
upon  the  hinge-pin  H  or  the  cam-latch  shaft.  The  block  is 
opened  by  pressing  the  thumb-piece  forward,  which  dis- 
engages the  cam-latch  from  its  recess.  When  the  block 
has  nearly  completed  its  rotation  upward,  it  strikes  against 
the  projecting  lug,  e,  of  the  extractor  E,  Fig.  317,  and  rotates 
the  latter  slowly,  thus  extracting  the  empty  case.  The 
ejector  then  acts  as  before  explained,  and  throws  the  case 
out  of  the  receiver. 


320.  Breech  Mechanism  of  the  Cal.  .30  Rifle  —  The  Bolt. 

This  mechanism  belongs  to  the  system  in  which  the 
block  slides  parallel  to  the  axis  of  the  bore,  and  the  gun  is 
a  bolt-gun. 

The  principal  parts  are  : 


SMALL   ARMS. 


555 


The  bolt  A  Fig.  319; 
The  sleeve  /,  Fig.  320; 
The  extractor  E,  Fig.  321. 

THE  BOLT,  Fig.  319,  is  a  hollow  cylinder,  closed  at  the 
front  end  except  a  small  opening,  /',  in  the  centre,  for  the 


FIG.  319. 

passage  of  the  point  of  the  firing-pin.  Its  interior  shape  is 
shown  in  section,  Fig.  336. 

The  head  of  the  cartridge  rests  against  the  front  of  the 
bolt,  which  is  hollowed  to  receive  it,  and  which  supports 
the  pressure  of  the  powder-gas,  a  is  the  locking-lug,  which 
engages  in  the  locking-recess  <z,  Fig.  313,  in  the  front  part 
of  the  receiver ;  r  is  the  guide-rib  which  rests  against  the  left 
side,  r,  of  the  guide-groove,  Fig.  313,  when  the  bolt  is  un- 
locked and  rotated,  and  guides  the  motion  of  the  bolt.  It 
also  forms  a  stop  to  limit  the  motion  when  the  bolt  is 
rotated  in  opening.  The  guide-rib  has  a  shoulder,  e,  in  front, 
against  which  a  corresponding  shoulder  on  the  extractor 
rests. 

The  rear  end,  s,  of  this  rib  rests  in  front  of  a  correspond- 
ing shoulder,  j,  Fig.  313,  on  the  receiver,  when  the  block  is 
locked  for  firing,  and  forms  a  safety-support  to  resist  the 
pressure,  the  lug  a  being  the  first  support.  D  is  the  body 
of  the  bolt,  in  one  piece  with  the  operating-handle  //.  This 
handle  terminates  at  the  bolt,  in  a  collar,  d,  Fig.  319,  which 
only  partly  encircles  the  rear  end  of  the  bolt. 

This  collar  serves  to  connect  the  bolt  with  the  other 
parts  of  the  mechanism. 


556  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY, 

The  rear  side,  //,  of  the  operating-handle  7i,  rests  in  front 
of  a  corresponding  shoulder,  //,  Fig.  313,  in  the  receiver  in 
the  firing  position,  and  forms  a  second  safety-support  to  re- 
sist the  pressure. 

At  the  rear  end  of  the  bolt  is  a  notch,  k,  one  side  be- 
ing straight  and  the  other  inclined.  This  notch  cocks  the 
firing-pin  when  the  bolt  is  rotated  in  opening,  and  also 
allows  the  cocking-piece,  carrying  forward  the  firing-pin 
and  striker,  to  move  down  into  it,  when  the  piece  is  dis- 
charged, as  will  be  explained 

There  is  also  a  longitudinal  groove,  j,  its  rear  end  turn- 
ing to  one  side,  and  its  front  end  terminating  abruptly  in  a 
shoulder. 

This  groove  works  the  ejector-lever  /,  Fig.  313,  in  the 
bottom  of  the  receiver.  The  notch  i '  admits  a  stud,  i' ',  Fig. 

320,  on  the  sleeve,  and  the  notch  /  is  for  the  safety-lock  /, 
Fig.  320. 

321.  Breech  Mechanism  Cal.  .30— The  Sleeve— The  Extractor. 


THE  SLEEVE  (Fig.  320)  serves  to  connect  the  firing 
mechanism  and  the  bolt,  and  carries  the  safety-lock  and  the 
extractor.  It  consists  of  a  single  piece  of  metal,  the  lower 
parts,  a  and  c,  of  which  are  hollow  cylinders,  and  the  upper 
part,  /,  an  arm  of  the  shape  indicated.  The  firing-pin  and 
cocking-piece  Fk,  Figs.  323  and  336,  pass  through  the  cylin- 
ders ac,  and  the  slot  k,  in  c,  is  to  allow  the  hammer  to  move 
forward  and  back  in  firing  and  cocking.  The  stud  i'  enters 
the  notch  /',  Fig.  319,  in  the  interior  of  the  bolt,  and  locks 
the  bolt  and  sleeve  on  the  interior.  The  arm  /  has  a  cut, 
d,  which  embraces  the  circular  collar  d,  Fig.  319,  on  the 
bolt,  and  locks  the  sleeve  and  bolt  together  on  the  exterior. 


SMALL   ARMS.  55/ 

This  locking  on  the  interior  and  exterior,  allows  the  oolt  to 
turn,  while  the  sleeve  remains  fixed,  but  does  not  allow 
longitudinal  motion  of  the  bolt  without  the  sleeve.  The 
fork  e  in  front  carries  the  extractor  £,  which  is  secured  in 
it  by  a  screw  i.  The  shoulder  g  forms  a  seat  for  the  spiral 
main  spring  6",  Fig.  323,  which  surrounds  the  firing-pin 
F.  The  safety-lock  is  shown  in  rear.  It  consists  of  a 
thumb-piece,  L,  and  spindle,  /.  Its  object  is,  first,  to  lock 
the  bolt  in  the  firing  position,  so  that  the  breech  cannot  open 
accidentally ;  and  second,  to  lock  the  firing-pin  in  the  full-cock 
position,  so  that  the  piece  cannot  be  accidentally  discharged. 
Both  these  operations  are  performed  at  the  same  time,  as 
follows : 

The  spindle  /is  half  cut  away,  as  explained  in  the  case 
of  the  magazine  cut-off.  The  thumb-piece  L  is  cut  away 
also,  so  that  when  turned  to  the  left  the  cut-away  portion 
forms  part  of  the  interior  surface  of  the  cylinder  c,  through 
which  the  cocking-piece  can  pass  freely.  When  in  this  posi- 
tion also,  the  cut-away  part  of  the  spindle  /  forms  part  of  the 
interior  surface  of  the  cut  d,  and  the  collar  d,  Fig.  319,  on 
the  bolt  can  rotate  freely  in  this  cut.  When  the  thumb-piece 
L  is  turned  to  the  right,  the  cut-away  part  no  longer  forms  a 
portion  of  the  interior  surface  of  the  cylinder  c,  and  hence  the 
cocking-piece  cannot  enter  this  cylinder  to  move  forward. 
At  the  same  time,  the  rounded  part  of  the  spindle  /,  turns 
down  into  the  cut  d,  and  its  .front  end  enters  the  notch  /, 
Fig.  319,  in  the  bolt,  thus  preventing  the  latter  from  rotating. 
The  rear  end  of  the  bolt  fits  against  the  shoulder  o,  so  that 
the  exterior  of  the  cylinder  c  and  the  exterior  of  the  bolt 
form  one  continuous  surface. 

The  cylinder  a  enters  the  interior  of  the  bolt. 

THE  EXTRACTOR  (Fig.  321)  is  a  long  bar,  E,  having  a 
hook,  0,  at  its  extremity  which  engages  over  the  rim  of  the 
cartridge.  It  is  attached  at  the  other  extremity  to  the 
sleeve  /,  as  already  explained,  e  is  a  projection  which  rests 
against  a  corresponding  shoulder,  ^,  on  the  guide-rib  r,  of 
the  bolt,  Fig.  319.  q  is  a  recess  fitting  against  a  shoulder,  r, 
in  the  receiver,  Fig.  313,  in  the  locked  position,  and  /  a 
spring  which  acts  against  the  lower  surface  of  q  on  the  re- 


558  TEXT-BOOK   OF  ORDNANCE  AND    GUNNERY. 

ceiver,  to  force  the  extractor  down  over  the  rim  of  the  car- 
tridge. The  extractor  has  a  slight  motion  around  the  screw 
i,  which  is  necessary  in  dismounting  the  mechanism. 


FIG.  321. 

322.  Firing  Mechanism — General  Principles — Conditions  for  Good 
Firing  Mechanism — Firing  Mechanism  of  Springfield  Rifle. 

The  ammunition  used  with  all  modern  small  arms  con- 
tains a  central  primer  of  mercuric  fulminate,  which  is  ignited 
by  a  blow  from  the  firing  mechanism. 

The  method  generally  adopted  is  to  transmit  this  blow 
through  the  medium  of  a  firing-pin  passing  through  the 
breech,  mechanism.  The  pin  may  be  acted  on  directly  by  a 
spring  which  forces  it  forward  when  the  trigger  is  pulled, 
or  it  may  be  acted  on  by  a  hammer  which  is  itself  acted  on 
directly  by  a  spring:  The  first  method  is  that  now  generally 
adopted  for  bolt-guns,  the  second  being  used  in  the  Spring- 
field and  some  older  forms  of  breech-loaders. 

CONDITIONS  TO  BE  FULFILLED  BY  A  GOOD  FIRING  MECH- 
ANISM.—A  good  firing  mechanism  should  fulfil  the  following 
conditions  : 

1.  It  should  ignite  the  primer  with  certainty  and  without 
piercing  it. 

2.  It  should  not  be  hard  to  operate,  as  this  causes  loss  of 
aim  ;   nor  too  easy,  as  this  leads  to  accidents. 

3.  Its  parts  should   be  simple,  strong,   few  in  number, 
easily  dismounted  and  assembled,  and  interchangeable. 

4.  It  should  be  cocked  automatically  by  the  opening  or 
closing  of  the  breech.     The  reasons  why  cocking  on  open- 
ing is  preferred  have  been  given. 

5.  It  should  have  a  safety-device  to  prevent  accidental 


SMALL    ARMS. 


559 


discharge  when  the  piece  is  carried  loaded,  and  should  show 
clearly  whether  it  is  cocked  or  not. 

FIRING  MECHANISM  OF  SPRINGFIELD  RIFLE. — The  prin- 
cipal parts  of  this  mechanism  are  (Fig.  322) : 

The  firing  pin  F\ 

The  hammer  b  ; 

The  tumblers; 

The  main  spring  d\ 

The  sear  e  and  sear-spring  e' ; 

The  trigger/. 


FIG.  322. 

The  firing-pin  F  passes  through  the  breech-block  Z>,  and 
projects  to  the  rear.  The  hammer  b  is  fastened  to  the  tum- 
bler c  by  the  tumbler-screw,  and  fits  on  a  square  arbor  or 
shaft,  so  that  the  hammer  and  tumbler  must  rotate  together. 
The  tumbler  has  three  notches:  a  full-cock,  i  ;  half-cock,  2; 
and  safety-notch,  3.  The  main  spring  d  is  attached  to  the 
tumbler  by  a  swivel,  d'.  The  sear  e  is  a  pivoted  lever,  and 
is  acted  on  by  the  sear-spring  /,  which  forces  it  against  the 
tumbler,  and  hence  it  is  always  ready  to  catch  in  one  of  the 
notches  I,  2,  or  3.  The  trigger  f  is  a  pivoted  lever,  and 
acts  against  a  projection  on  the  long  arm  of  the  sear.  The 
tumbler  and  sear  are  held  in  place,  and  supported  on  the 
inside,  by  a  piece  called  the  bridle,  not  shown  in  the  figure. 


l^EXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


All  the  parts  except  the  firing-pin  and  trigger  are  assem- 
bled to  a  flat  plate,  a,  called  the  lock-plate,  which  is  secured 
to  the  right  side  of  the  gun  by  two  screws. 

ACTION  OF  THE  MECHANISM. — When  the  trigger  /  is 
pulled  in  the  direction  of  the  arrow  i,  the  sear  is  withdrawn 
from  its  notch  in  the  tumbler,  and  the  action  of  the  main 
spring  causes  the  hammer  and  tumbler  to  rotate  in  the  di- 
rection of  the  arrowy,  striking  a  blow  upon  the  firing-pin, 
which  is  thus  driven  forward  against  the  primer,  explod- 
ing it. 

323.  Firing  Mechanism  of  the  Cal.  .30. 

The  principal  parts  of  this  mechanism  are  (Fig.  323)  r 
The  firing-pin  F  and  striker  F' ; 
The  main  spring  G  ; 
The  cocking-piece  K '; 
The  sear  H  and  sear-spring  H' ; 
The  trigger  T. 


K 


FIG.  323. 


The  firing-pin  is  composed  of  two  parts,  the  body  F  and 
the  striker  F ',  the  method  of  connection  of  the  two  being 
indicated  in  the  figure.  The  striker  can  thus  be  readily 
replaced  when  broken,  or  removed  to  permit  the  replacing 
of  a  broken  main  spring.  The  firing-pin  passes  through  the 
sleeve  /  and  the  bolt,  as  already  explained,  and  the  main 
spring  G  rests  between  the  rear  shoulder  of  the  striker  F> 


SMALL   ARMS.  561 

and  the  front  shoulder^- on  the  sleeve,  Fig.  320.  It  is  evident 
that  when  the  firing-pin  is  drawn  back,  the  main  spring  will 
be  compressed,  since  the  sleeve  /  is  fixed  with  reference  to 
the  Din.  The  cocking-piece  K  is  screwed  to  the  rear  end  of 
the  firing-pin.  The  part  g  is  roughened  to  give  a  firm  hold 
to  the  fingers  in  cocking.  The  part  k  carries  the  full-cock 
notch  i  and  the  wedge-shaped  cocking-nose  j,  all  these 
being  in  one  piece.  The  cocking-nose  j  engages  in  the 
notch  k,  Fig.  319,  in  the  rear  end  of  the  bolt. 

The  sear  H  is  a  piece  of  metal  of  the  shape  shown, 
hinged  at  a  to  the  receiver,  and  its  nose  c,  passing  through  a 
cut  in  the  bottom  of  the  receiver,  engages  in  the  full-cock 
notch  i.  It  is  constantly  pressed  upward  into  this  notch  by 
the  spiral  sear-spring  H',  one  end  of  which  bears  against 
the  receiver,  and  the  other  against  the  sear.  The  trigger  T 
is  pivoted  to  the  sear.  At  the  rear  it  rests  against  the 
bottom  of  the  receiver,  at  the  point  m,  and  after  the  trigger 
is  pulled  slightly  the  point  n  comes  into  bearing  against  the 
bottom  of  the  receiver,  the  point  m  losing  contact. 

ACTION  OF  MECHANISM.  —  Suppose  the  piece  fired. 
When  the  bolt  is  rotated  to  the  left  by  its  operating-handle, 
the  inclined  side  of  the  notch  k,  Fig.  319,  in  the  bolt,  presses 
against  the  corresponding  side  of/,  Fig.  323,  and  forces  the 
cocking-piece,  firing-pin,  and  striker  backward,  till  the  end 
of  j  rests  against  a  notch  on  the  rear  end  of  the  bolt.  The 
firing-pin  is  thus  drawn  back  and  cocked,  the  main  spring  G 
being  compressed. 

After  the  introduction  of  the  cartridge  into  the  receiver, 
the  bolt  is  pushed  forward  and  rotated  to  the  right,  to 
lock  it. 

In  moving  forward,  the  full-cock  notch  catches  against 
the  sear  H,  and  the  firing-pin  is  now  held  back  by  the  sear. 
When  the  bolt  is  rotated  to  the  right  for  locking,  the  slight 
forward  motion  completes  the  compression  of  the  main 
spring,  and  the  rotation  brings  the  nose/  and  part  k  of  the 
cocking-piece  opposite  the  notch  k,  Fig.  319,  in  the  bolt 
When  the  trigger  is  pulled  in  the  direction  of  the  arrow,  the 
nose  c  of  the  sear  is  lowered  slowly  at  first  out  of  the  full- 
cock  notch  i.  As  the  pull  of  the  trigger  continues,  the  point 


$62  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

m  loses  its  bearing  against  the  bottom  of  the  receiver,  and 
the  point  n  comes  into  bearing.  The  lever-arm  being  thus 
increased,  the  nose  of  the  sear  at  the  last  moment,  moves 
quickly  out  of  its  notch  i ;  the  firing-pin  is  forced  forward 
under  the  action  of  the  main  spring  G,  and  the  cartridge  is 
fired.  If  the  bolt  is  not  properly  locked,  the  notch  kt  Fig. 
319,  on  the  bolt  will  not  be  opposite  the  nosey,  Fig.  323,  of 
the  cocking-piece,  and  the  latter  either  cannot  move  for- 
ward sufficiently  far  to  allow  the  firing-pin  to  strike  the 
primer,  or,  if  the  bolt  is  nearly  locked,  the  forward  motion 
of  the  cocking-piece  will  causey  to  strike  the  inclined  side 
of  the  notch  k,  Fig.  319,  and  thus  cause  the  bolt  to  rotate  to 
the  right,  and  completely  lock  it.  This  is  an  additional 
safety-device. 

324.  Sights— General  Principles — Position. 

There  are  two  sights  for  small  arms : 

1.  An  adjustable  rear  sight- 

2.  A  fixed  front  sight. 

REAR  SIGHTS. — A  good  rear  sight  for  a  military  arm 
should  be  simple,  solid,  easy  of  repair,  graduated  so  that 
the  marks  can  be  readily  seen,  and  so  arranged  that  when 
the  rear-sight  notch  is  set  to  any  particular  graduation  it 
will  not  be  displaced  by  the  shock  of  firing,  or  by  any  other 
means,  except  when  changed  by  the  firer.  The  form  of  the 
notch  should  be  such  as  to  enable  the  target  to  be  seen  easily. 

It  should  be  out  of  the  way  and  well  protected  when  not 
in  use,  to  avoid  being  broken,  and  it  should  contain  all  the 
graduations  required  up  to  the  extreme  effective  range  of 
the  arm.  The  requisite  of  simplicity,  excludes  peep  and 
telescope  sights,  except  for  selected  marksmen,  and  the  flat 
trajectories  of  the  small-calibre  rifles  have  greatly  simplified 
the  rear  sights  by  reducing  their  heights,  and  doing  away 
with  corrections  for  wind,  and  to  some  extent  for  drift. 

Elevations  are  marked  in  ranges  and  not  in  degrees,  as 
the  ammunition  is  invariable. 

The  rear  sight  generally  consists  of  a  leaf  which  is 
hinged  to  a  base,  the  latter  being  screwed  to  the  barrel  of 
the  gun. 


SMALL   ARMS.  $63 

The  base  carries  a  flat  spring  which  bears  against  the 
lower  edge  of  the  leaf  and  keeps  it  upright  when  in  use,  or 
folded  down  against  the  base  when  not  required. 

The  leaf  is  graduated  in  ranges  (yards)  and  carries  a 
slide  wrhich  has  a  notch  cut  m  it  forming  the  rear-sight 
notch. 

This  slide  moves  along  the  leaf,  and  is  clamped  at  any 
graduation  and  held  firmly  in  place. 

FRONT  SIGHT. — The  front  sight  is  generally  a  stud  set 
at  the  muzzle,  and  terminates  in  a  thin  edge  parallel  to  the 
axis  of  the  bore.  It  should  be  sufficiently  strong,  to  pre- 
vent injury  by  the  rough  usage  of  service. 

POSITION. — The  front  and  rear  sights  are  generally 
so  placed,  that  the  notch  of  the  rear  sight,  and  top  of  the 
front  sight,  shall  be  in  a  plane  passing  through  the  upper 
element  of  the  barrel  and  the  axis  of  the  bore,  and  at  as 
great  a  distance  apart  as  possible,  so  as  to  give  the  longest 
sight-radius  attainable,  consistently  with  distinct  vision  of 
the  target  and  the  two  sights.  In  some  arms,  as  the  Spring- 
field, the  rear  sight  has  an  arrangement  for  correcting  for 
wind,  and  the  slide  is  set  with  an  inclination  to  the  left 
equal  to  the  permanent  angle  of  drift. 

325.  Sights  for  Springfield  Rifle— Sights  for  the  Cal.  .30. 

SIGHTS  FOR  SPRINGFIELD  RIFLE. —  Rear  Sight. — The 
principal  parts  are  (Fig.  324) : 

The  fixed  base  A  ; 

The  movable  base  and  spring  B\ 

The  sight-leaf  C\ 

The  sight-leaf  slide  D. 

The  fixed  base  A  is  screwed  to  the  barrel.  The  movable 
base  B  carries  a  flat  spring,  which  bears  against  the  lower 
edge  of  the  sight-leaf  C  and  keeps  it  vertical  or  folded 
down.  This  movable  base  rotates  about  the  pivot  E,  and  is 
moved  by  the  screw  F  working  in  a  worm  on  the  end  of  B. 
The  sight-leaf  is  thus  moved  to  right  or  left,  and  corrections 
made  for  wind.  The  sight-leaf  C  carries  the  graduations, 
and  is  hinged  to  the  movable  base  at  G.  It  also  carries  the 


564  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

binding-screw  //",  which  can  be  made  to  bear  against  the 
sight-leaf  slide,  and  thus  clamp  it  in  any  position. 

The  sight-leaf  slide  D  carries  the  rear-sight  notches  i,  2, 
3,  4,  and  5.  No.  5  is  used  for  ranges  up  to  200  yards  with 
the  leaf  down. 


FIG.  324. 

For  distinction  Nos.  i  and  3  will  be  called  peep-sights, 
and  Nos.  2  and  4  open  sights. 

If  the  peep-sights  i  and  3  are  to  be  used,  No.  i  is  em- 
ployed from  200  to  1350  yards,  the  right-hand  arrow  on 
No.  i  coinciding  with  the  graduations. 

For  1400  yards  the  leaf-slide  is  pushed  down,  and  No.  3 
is  used,  its  mark  coinciding  with  the  graduation  14. 

From  this  to  2000  yards  the  left-hand  arrow  on  No.  i 
coincides  with  the  left-hand  graduations,  the  sight  being 
taken  through  No.  3. 

If  the  open  sights  2  and  4  are  to  be  used,  No.  2  is 
employed  from  200  to  1400  yards.  The  leaf-slide  is  then 
pushed  down,  and  No.  4  is  used,  the  left-hand  arrow  on  No. 
2  coinciding  with  the  left-hand  graduations.  The  correc- 
tions for  wind  are  marked  on  the  fixed  base,  and  the  leaf- 


SMALL   ARMS. 


565 


slide  is  set  at  an  inclination  to  the  left  equal  to  the  perma- 
nent angle  of  drift. 

Front  Sight. — The  front  sight,  Fig.  324,  consists  of  a  thin 
blade,  /,  set  in  a  stud. 


FIG.  325. 

SIGHTS  FOR  CAL.  ,.30. — Rear  Sight. — The  principal  parts 
are  (Fig.  325) : 

The  fixed  base  and  spring  A  ; 

The  leaf  5; 

The  leaf-slide  C. 

The  fixed  base  is  screwed  to  the  barrel,  and  carries  the 
flat  spring  which  bears  against  the  lower  edge  of  the  leaf 
B,  and  keeps  it  upright  or  folded.  The  leaf  B  is  hinged  to 
the  base  at  d  and  is  graduated  on  both  sides,  beginning  with 
700  yards.  From  300  to  600  yards  the  fixed  base  is  cut  in 
steps,  and  the  steps  marked  as  in  the  figure.  For  ranges  up 
to  600  yards,  the  leaf  is  folded  down,  and  the  slide  C  rests 
upon  the  corresponding  step,  the  sight  being  taken  through 
the  notch  e.  Beyond  600  yards  the  leaf  is  upright,  the  top 
surface  of  the  slide  coinciding  with  the  graduation,  and  the 
sight  is  taken  through  the  notch/.  The  slide  C  is  clamped 
in  place  by  a  serrated  piece  contained  in  the  slide,  and  acted 
on  by  a  spiral  spring  which  presses  it  constantly  against 
notches  on  the  right-hand  inner  edge  of  the  leaf. 


566  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

A  pressure  on  the  button  g  releases  this  catch,  and  the 
slide  may  be  moved  up  or  down.  The  arrangement  is  shown 
in  section  in  the  figure. 

The  notch  e  is  set  slightly  to  the  left  of  the  axis  of  the 
bore  and  corrects  for  drift  at  500  yards.  For  distances  less 
than  500  yards  this  correction  is  too  great,  and  for  those 
greater  than  500  yards  too  small. 

The  notch /is  similarly  set  to  the  left  of  the  axis  of  the 
bore  and  corrects  for  drift  at  1000  yards.  For  distances  less 
than  this  the  correction  is  too  great,  and  for  distances 
greater  than  1000  yards,  too  small.  The  notches  on  the  leaf 
and  slide  are  exactly  similar  to  those  on  the  sight  of  the 
Springfield  rifle. 

FRONT  SIGHT. — This  is  shown  at  F.  It  resembles  the 
Springfield  front  sight,  and  differs  from  it  principally  in 
"being  higher. 

326.  The  Stock  and  Mountings. 

THE  STOCK.— The  stock  is  that  part  of  the  arm  to  which 
all  the  other  parts  are  assembled,  and  it  serves — 

1.  To  facilitate  the  handling  and  pointing,  to  diminish 
the  shock  of  recoil  by  distributing  it  over  a  greater  area  at 
the  shoulder,  and  to  stiffen  and  protect  the  barrel. 

2.  In  some  magazine  arms  to  carry  the  supply  of  am- 
munition required  for  rapid  fire,  and  in  all  arms  to  carry 
certain  parts  necessary  for  the  service,  security,  or  preserva- 
tion of  the  piece. 

For  lightness  it  is  made  of  wood,  and  for  strength  this 
wood  should  be  of  close  grain,  and  it  should  be  well  sea 
soned  to  prevent  warping ;  walnut  is  generally  used. 

It  is  widened  at  the  butt,  a,  Fig.  326,  to  distribute  the" 


^~~ 


FIG.  326. 

pressure  of  recoil  over  the  shoulder,  and  is  crooked  at  the 
small  of  the  stock,  b,  for  convenience  of  aiming.     This  crook 


REPEATING    OR   MAGAZINE   ARMS.  $6? 

must  not  be  excessive,  as  it  causes  rotation  about  the 
shoulder,  with  a  lever-arm,  ac,  which  increases  with  the 
crook,  and  may  cause  inconvenience.  It  also  weakens  the 
stock,  since  the  wood  is  cut  across  the  grain  at  this  point. 

In  some  cases,  to  avoid  this  weakening  and  give  room 
for  the  mechanism,  the  stock  is  made  in  two  distinct  parts, 
called  respectively  the  butt-stock  and  the  tip-stock.  With 
smokeless  powders,  the  barrel  becomes  excessively  heated  ; 
and  to  prevent  contact  with  the  hand,  the  upper  part  of  the 
barrel,  at  the  rear,  is  also  covered  with  wood. 

Under  the  head  of  mountings  are  included  the  wiping, 
rod,  the  bands  and  tip,  the  butt-plate,  trigger-guard,  swivels, 
and  the  various  pins  and  screws  by  which  these  parts  are 
secured  to  the  gun. 

The  wiping-rod  is  screwed  into  its  seat  for  a  short  dis- 
tance, to  avoid  displacement  in  firing. 

The  bands  assemble  the  barrel  to  the 
stock,  and  are  not  continuous,  but  split,  Fig. 
327,  and  are  assembled  by  a  screw,  a.  They 
can  thus  be  readily  adjusted  to  the  stock 
and  barrel,  and  any  undue  binding  prevented, 
as  this  might  cause  vibration  in  firing. 

The  butt-plate  and  trigger-guard  preserve 
the  butt  and  trigger  respectively  from  wear 
and  accident,  and  the  swivels  are  used  for        FIG.  327. 
stacking  and  to  support  the  gun-sling. 


REPEATING  OR  MAGAZINE  ARMS. 

327.  Advantages  of  Magazine  Arms— Definition— Conditions  to  be 
fulfilled  by  a  Good  Magazine  Arm. 

ADVANTAGES. — In  ordinary  breech-loaders  three  opera- 
tions are  necessary  to  prepare  for  firing : 

1.  Open  the  breech  ; 

2.  Insert  the  cartridge  ; 

3.  Close  the  breech. 

The  longest  of  these  is  the  time  required  to  take  the 
cartridge  from   the  box  or  belt  and  insert  it  in  the  gun. 


568  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  rapidity  of  fire  is  therefore  greatly  increased  if  the 
cartridges  can  be  automatically  introduced,  and  the  three 
operations  reduced  to  two,  viz.,  opening  and  closing  the 
breech. 

As,  however,  the  cartridges  so  introduced  must  be  carried 
by  the  piece  in  some  convenient  receptacle,  it  is  evident  that 
the  number  so  carried  is  limited,  and  hence  automatic  intro- 
duction of  the  cartridges  cannot  be  continuous  beyond  a 
few  shots. 

The  advantage  of  a  magazine  arm  is,  then,  that  it  can 
furnish  a  certain  number  of  shots  in  a  very  small  interval  of 
time ;  and  in  order  to  make  use  of  this  advantage  it  is  neces- 
sary to  be  able  to  reserve  this  supply  till  needed,  and  ordi- 
narily to  use  the  arm  as  a  single-loader. 

This  leads  to  the  conclusion  that  a  good  magazine  arm 
should  be  also  a  good  single-loader,  and  should  fire  as 
rapidly,  when  used  as  such,  as  any  good  single-loader,  since 
the  arm  is- used  habitually  as  such,  and  only  in  emergencies 
as  a  magazine  gun. 

DEFINITION. — A  magazine  or  repeating  arm  may  then  be 
defined  as  one  in  which  a  certain  number  of  cartridges  are 
introduced  in  succession,  automatically  and  rapidly,  into  the 
receiver. 

CONDITIONS  TO  BE  FULFILLED  BY  A  GOOD  MAGAZINE 
GUN. — A  good  magazine  gun  should  fulfil  the  following 
conditions : 

1.  When  used  as  a  single-loader  it  should  fire  as  rapidly 
as  any  ordinary  single-loader. 

2.  When  used  as  a  magazine  'arm  it  should   give   the 
greatest  possible  rapidity  of  fire,  and  the  mechanism  should 
work  well  and  regularly  when  rapidly  used. 

3.  It   should   allow   the   change   from   single-loader   to 
magazine  fire  to  be  readily  and  quickly  made,  and  the  de- 
vice for  making  this  change  should  be  readily  seen,  so  that 
no  mistake  can   be   made ;  and  so  placed  that  it  cannot  be 
accidentally  operated. 

4.  It  should  afford  an  easy  and  rapid  method  of  recharg- 
ing the  magazine. 

5.  The  cartridges  in  the  magazine  must  not  be  damaged 


RE  PEA  TING    OR   MA  GA  ZINE  A  RMS. 


569 


or  deformed  by  firing  or  by  handling  the  piece,  or  be  liable 
to  explode  by  the  shock  of  discharge. 

6.  The  weight  of  the  piece  with  magazine  and  cartridges 
must  not  exceed  that  usually  allowed  for  small  arms. 

7.  It  should  afford  a  ready  view  of  the  number  of  car- 
tridges in  the  magazine  at  all  times,  so  that  the  supply  may 
not  be  exhausted  before  they  are  needed. 

328.  Classification  of  Repeating  Mechanism. — The  Detachable  Maga- 
zine— Lee  Magazine — Advantages  and  Disadvantages  of  De 
tachable  Magazines. 

CLASSIFICATION. — The  repeating  mechanism  includes  the 
magazine  in  which  the  supply  of  cartridges  is  carried,  and 
the  means  by  whic'h  the  supply  is  fed  to  the  receiver.  As 
these  are  generally  combined,  it  is  customary  to  classify  the 
mechanisms  according  to  the  magazines  used. 

Magazines  are  classified  into — 

1.  Detachable  ; 

2.  Fixed. 

DETACHABLE  MAGAZINES. — The  detachable  magazines 
are  generally  box-shaped,  and  are  placed  in  rear  of  the 
barrel  and  below  the  receiver.  They  are  called  detachable 
because  they  may  be  readily  detached  from  the  gun.  They 


,b    a 


are  generally  made  of  thin  sheet  steel,  and  contain  a  spring 
or  some  device  by  which  the  cartridges  are  constantly 
pressed  upward  toward  the  receiver.  The  top  of  the 
magazine  is  folded  over  for  a  short  distance  at  the  rear,  a, 
Fig.  328,  and  these  folds  hold  the  cartridges  in  place  against 


570  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

the  action  of  the  spring.  When  the  bolt  is  drawn  to  the 
rear  over  the  cartridge,  a  portion,  b,  of  its  rim  projects  be- 
yond the  folds.  As  the  bolt  is  pushed  forward,  it  strikes 
the  rim  b  and  pushes  the  cartridge  forward  beyond  the  folds, 
out  of  the  magazine  and  into  the  receiver  and  chamber. 
This  device  in  some  similar  form  is  found  in  all  box  maga- 
zines. 

LEE  MAGAZINE.— The  Lee  magazine  is  a  good  example 

of  this  system,  and  is  shown  in  Fig.  329  with  its  method,  of 
attachment  to  the  gun. 


FIG.  329. 

a  is  the  magazine,  b  a  projection  on  its  rear  end,  c  the 
magazine-catch  operated  by  the  U-shaped  sear-spring  d,  e  a 
folded  spring  which  pushes  the  cartridges  upward.  The 
filled  magazine,  containing  five  cartridges,  is  inserted  from 
below,  in  a  cut  made  for  it  in  the  stock  and  receiver,  and 
pushed  upward  till  the  magazine-catch  c  snaps  under  the 
projection  b.  When  the  magazine  is  empty  it  is  released  by 
pressing  on  the  magazine-catch  c,  and  withdrawn. 

ADVANTAGES. — These  are  : 

1.  Since  they  can  be  used  only  when  fixed  in  place,  it  is 
always  evident  whether  or  not  the  magazine  supply  is  being 
employed.     This  does  not,  however,  apply  to  those  which 
are  lowered  vertically  to  cut  off  the  supply. 

2.  A  number  of  these  can  be  carried  loaded,  and  as  they 


REPEATING    OR   MAGAZINE  ARMS.  $?I 

can  be  inserted  quickly,  the  rapid  fire  can  be  kept  up  con 
tinuously  for  some  time. 

DISADVANTAGES. — i.  The  magazine  has  considerable 
weight  and  adds  to  the  burden  carried  by  the  soldier.  This 
additional  weight  could  otherwise  be  utilized  to  increase 
the  number  of  cartridges  carried. 

2.  The  magazines  are  apt  to  be  thrown  away  or  lost 
when  empty,  and  when  lost  the  gun  cannot  be  used  as  a 
magazine  arm. 

3.  The  cut  through  the  bottom  of  the  receiver  is  incon- 
venient when  the  gun  is  used  as  a  single-loader,  and  when 
the  magazine  is  attached  it  must  generally  be  used ;  that  is, 
the  gun  cannot  be  used  with  facility  as  a  single-loader. 

To  remedy  the  inconvenience  of  the  cut  in  the  receiver, 
the  Lee  gun  has  a  spring  slide  which  closes  this  cut  as  soon 
as  the  magazine  is  withdrawn,  and  the  insertion  of  the 
magazine  pushes  this  slide  out  of  the  way.  In  some  guns 
of  this  type  a  cut-off  is  arranged  by  which  the  magazine  is 
lowered  vertically,  so  that  the  cartridges  will  be  out  of  the 
way  of  the  bolt  when  the  gun  is  to  be  used  as  a  single- 
loader. 

329.  Fixed  Magazines — Classification — Description  of  the  Jarmann 
Magazine. 

CLASSIFICATION. — Fixed  magazines  may  be  classified 
according  to  their  shape  into — 

1.  Tubular; 

2.  Box. 

Tubular  magazines  may  be  placed  either  under  and 
parallel  to  the  barrel,  in  the  front  part  of  the  stock ;  or  in 
the  butt,  in  rear  of  the  barrel. 

Box  magazines  are  placed  in  rear  of  the  barrel,  and 
directly  in  front  of  the  trigger-guard. 

TUBULAR  MAGAZINE  UNDER  BARREL — JARMANN  MAGA- 
ZINE.— The  Jarmann  magazine-gun,  formerly  used  in  Nor- 
way, may  be  taken  as  an  example  of  the  tubular  magazine  un- 
der the  barrel.  In  Fig.  330,  a  is  the  barrel ;  b  the  magazine  ;  c 
the  spiral  spring  which  forces  the  cartridges  to  the  rear ;  d 
the  piston  attached  to  the  end  of  the  spring ;  e  the  carrier 


572  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

which  lifts  the  cartridges  from  the  mouth  of  the  magazine 
to  the  receiver  ;  /  the  carrier-spring,  which  is  fork-shaped 
and  rests  on  two  pins,^-,  pressing  the  carrier  down  ;  h  the  pin 
by  which  the  carrier  is  attached  to  the  receiver,  and  around 


FIG.  330. 

which  it  rotates  ;  i  a  shoulder  on  the  rear  end  of  the  carrier, 
projecting  above  the  bottom  of  the  receiver  when  the  carrier 
is  down ;  j  a  corresponding  shoulder  and  recess  on  the  lower 
side  of  the  front  of  the  bolt,  which,  as  the  bolt  is  drawn  back 
allows  the  carrier  first  to  drop  under  the  action  of  the  spring 
/,  and  immediately  afterward,  as  the  bolt  moves  further 
back,  strikes  against  i  and  raises  the  carrier  ;  k  is  a  projec- 
tion from  the  lower  front  end  of  the  carrier,  whose  object  is 
to  work  the  cartridge-stop  and  hold  back  the  next  cartridge 
in  the  magazine.  This  projection  k,  carries  a  pin,  /,  which 
works  the  cartridge-stop. 

ACTION  OF  MECHANISM. — Suppose  the  piece  fired.  The 
breech  is  then  closed  by  the  bolt,  the  carrier  e  is  held  up  in 
the  position  shown  in  the  lower  figure  by  the  bearing  of  the 
lug  i  on  the  bottom  of  the  bolt.  The  carrier  thus  forms  a 
part  of  the  bottom  of  the  receiver.  The  cartridges  are  held 
back  in  the  magazine  against  the  action  of  the  spring  c,  by 
the  projection  k  of  the  carrier,  bearing  on  the  head  of  the 
rear  cartridge. 


REPEATING    OR   MAGAZINE  ARMS.  573 

As  the  bolt  is  withdrawn,  the  carrier  e  remains  in  the 
position  just  described,  because  its  lug  i  bears  continually 
against  the  bottom  of  the  bolt.  When  the  bolt,  in  its  back- 
ward motion,  reaches  a  position  such  that  the  cut/  comes 
over  the  lug  i  of  the  carrier,  the  latter  is  free  to  rotate,  and 
moves  downward  under  the  action  of  its  spring/.  During 
its  downward  motion  the  cartridges  are  kept  in  place  by 
the  bearing  of  the  front  of  the  carrier  e  against  the  head  of 
the  rear  cartridge.  At  the  last  moment  of  the  rotation  of 
the  carrier,  when  it  occupies  the  position  shown  in  the 
upper  figure,  this  bearing  is  removed,  and  the  rear  cartridge 
is  forced  by  the  spring  c,  out  of  the  magazine,  and  on  the 
carrier.  As  soon  as  this  is  done,  the  downward  rotation  of 
the  carrier  being  completed,  the  pin  /,  on  the  projection  k, 
strikes  the  cartridge-stop  m,  and  causes  it  to  rise  and  partly 
close  the  mouth  of  the  magazine,  thus  preventing  the  other 
cartridges  from  being  forced  out.  All  this  occurs  while  the 
cut/  in  the  bolt  is  over  the  lug  z  of  the  carrier.  As  the  bolt 
is  pulled  backward  still  further,  the  shoulder  of/  strikes  the 
shoulder  of  /  and  raises  the  carrier  e  with  its  cartridge 
quickly  to  the  mouth  of  the  chamber.  The  bolt  is  then 
pushed  forward  and  the  cartridge  inserted.  It  will  be  re- 
membered that  at  this  time  the  cartridges  are  held  back  in 
the  magazine  by  the  cartridge-stop.  To  release  this  stop, 
the  bolt,  in  moving  forward,  strikes  the  long  lever  n  of  the 
cartridge-stop,  which  is  situated  on  the  right-hand  side  of 
the  receiver.  This  pushes  the  lever  n  forward,  lowers  the 
stop,  and  frees  the  mouth  of  the  magazine,  and  under  the 
action  of  the  spiral  spring  c,  the  cartridges  move  forward  till 
the  head  of  the  rear  one  comes  into  bearing  against  the  pro- 
jection k,  which  is  now  in  the  position  shown  in  the  lower 
figure,  the  bolt  being  closed. 

The  principles  explained  here  are  found  in  modified 
forms  in  all  magazines  of  this  type.  The  magazine  has  a 
cut-oft  by  which  the  carrier  is  locked  in  its  upward  position 
and  the  gun  may  then  be  used  as  a  single-loader. 


574  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

330.  Objections  to  Tubular  Magazines  under  the  Barrel— Advan- 

tage. 

OBJECTIONS. — The  objections  to  tubular  magazines  under 
the  barrel  are  : 

1.  The  cartridges  lie  with  the  primer  of  one  against  the 
bullet  of  the  next,  and  hence  the  shock  of  discharge  is  liable 
to  explode  the  primer,  or  to  upset  and  deform  the  point  of 
the  bullet.     With  modern  smokeless  powders,  although  the 
bullet  is  not  so  liable  to  be  deformed,  owing  to  its  harder 
jacket,  it  is  more  liable  to  be  driven  down  into  its  case, 
since  any  excessive  crimping  of  the  bullet  to  the  case,  which 
would  tend  to  prevent  this,  increases  the  pressure  in  the 
gun,  by  increasing  the  resistance  to  motion  at  the  origin. 
If  the  bullet  be  forced  down  into  the  case,  the  density  of  load- 
ing of  the  charge  is  increased,  and  hence  also  the  pressure. 

2.  The  spiral  spring  which  forces  the  cartridges  into  the 
carrier,  must  be  long,  as  it  has  to  act  over  a  great  distance. 
Hence  it  is  tightly  compressed  at  first,  and  its  action  be- 
comes very  slight  on  the   last   cartridge,  and  is  therefore 
irregular. 

3.  When  the  magazine  is  full,  the  centre  of  gravity  of 
the  system  is  carried  forward,  and  as  it  is  emptied  this  cen- 
tre changes. 

4.  The  weight  of  the  arm  increases  considerably  when 
the  magazine  is  loaded. 

5.  The  magazine  is  difficult  to  load,  as  the  cartridges  must 
generally  be  inserted  singly. 

6.  The  state  of  supply  of  the  magazine  cannot  be  seen. 

7.  Unless  the  bolt  is  drawn  back  to  its  full  extent,  and 
quickly,  the  carrier  will  not  work  properly. 

8.  As  the  magazine-tube  is  thin,  a  slight  damage  to  the 
stock  may  close  up  the  tube  so  that  it  will  not  feed. 

Its  greatest  advantage  is  the  number  of  cartridges  car- 
ried. 

331.  Tubular    Magazine    in   Butt  —  Fixed  -  box  Magazines  —  The 

Mannlicher  Magazine. 

TUBULAR  MAGAZINE  IN   BUTT.— This  was  the  earliest 
form  of  magazine,  as  seen  in  the  Spencer  rifle,  which  was 


REPEATING    OR   MAGAZINE  ARMS. 


575 


used  during  the  Civil  War.  It  has  been  abandoned,  however, 
because  it  has  nearly  all  the  disadvantages  belonging  to  the 
tubular  magazine  under  the  stock,  and  in  addition  it 
weakens  the  small  of  the  stock  and  does  not  carry  a  large 
number  of  cartridges.  The  Hotchkiss  is  probably  the  best 
example  of  this  type. 

FIXED-BOX  MAGAZINE. — This  type  of  magazine  has  been 
adopted  by  many  of  the  foreign  powers  and  by  the  United 
States. 

THE  MANNLICHER  MAGAZINE. — The  Mannlicher  maga- 
zine may  be  taken  as  a  type  of  this  system  used  abroad. 


FIG.  331. 


In  Fig.  331,  a  is  the  fixed  box,  having  the  bottom  open 
at  b.  This  box  is  fixed  in  rear  of  the  barrel  and  in  front  of 
the  trigger-guard,  and  projects  below  the  stock  as  in  the 
Lee  magazine,  c  is  the  carrier-lever  ;  d  the  magazine-spring, 
which  pushes  the  carrier-lever  upward  against  the  car- 
tridges. The  cartridges  are  carried  in  a  packet,  e,  made  of 
tin,  the  top  and  bottom  edges  being  slightly  folded  over,  as 
shown  in  Fig.  328. 

This  packet  carries  five  cartridges,  and  is  inserted  with 
its  cartridges,  from  above,  through  the  cut  in  the  bottom  of 
the  receiver,  into  the  magazine  a.  It  is  held  in  place  in  the 
magazine,  by  the  upward  pressure  of  the  carrier-lever  c  on 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

the  cartridges,  which  is  transmitted  to  the  packet  e  by  the 
folded  edges,  and  as  this  would  push  the  packet  out  of  the 
magazine,  the  catch  /,  acted  on  by  the  spiral-spring  hy 
engages  against  a  lug,  g,  on  the  rear  end  of  the  packet,  and 
prevents  it  from  rising. 

ACTION  OF  THE  MAGAZINE. — When  the  filled  packet  e 
is  introduced  into  the  magazine,  it  compresses  the  magazine- 
spring  d.  The  packet  is  pushed  down  till  the  catch /snaps 
over  the  lug  g.  The  cartridges  being  constantly  pressed 
upward  by  c  and  d,  when  the  bolt  is  pushed  forward  it 
strikes  the  exposed  part  of  the  base  of  the  upper  cartridge, 
and  pushes  it  forward  beyond  the  folded  edges  of  the  case, 
the  surface/  of  the  receiver  guiding  the  point  of  the  bullet 
upward  and  into  the  chamber.  When  all  the  cartridges  are 
exhausted,  the  carrier-lever  c  and  spring  d  no  longer  exert 
an  upward  pressure  on  the  packet,  and  hence  the  latter  falls 
through  the  opening  b  in  the  bottom  of  the  receiver,  and 
thus  indicates  that  the  supply  is  exhausted. 

The  packet  may  be  removed  at  any  time  by  pressing  on 
the  projection  i  of  the  catch. 

To  cut  off  the  supply  the  packet  must  be  removed. 

332.  Advantages  and  Disadvantages  of  the  Fixed-box  Magazine, 
Mannlicher  Type  — General  Principles  of  the  Cal.  .30 
Magazine. 

ADVANTAGES.— The  Advantages  of  the  fixed-box  maga- 
zine, Mannlicher  type,  are : 

1.  In  common  with  all  box  magazines,  the  cartridges  lie 
so  that  the  spring  which  moves  them  acts  in  the  direction 
of  their  least  dimension,  and  therefore  the  great  length  and 
irregularity  of  its  action,  as  in  the  tubular  magazine,  are 
avoided. 

2.  The  cartridges  are  not  liable  to  explode,  or  to  be  de- 
formed in  handling  and  firing. 

3-  The  centre  of  gravity  of  the  system  is  not  changed. 

4-  The  magazine  is  easily  charged. 

5-  The  packets  are  light,  and   hence  do  not  add  much 
useless  weight  to  the  soldier's  burden,  and  they  are  cheap 
and  may  be  thrown  away. 


REPEATING    OR   MAGAZINE  ARMS.  S77 

6.  The    exhaustion    of    the  magazine    is    automatically 
indicated. 

7.  The   magazine   cannot   be  lost,  and  is  not  liable  to 
damage. 

DISADVANTAGES. — The  objections  are  : 

1.  When  the  packet  is  in  place  the  arm  cannot  be  used 
as  a  single-loader  without  great  care ;  and  when  the  packet 
is  withdrawn  the  bottom  of  the  receiver  is  not  solid,  which 
is  an  inconvenience. 

2.  The  cartridges  must  be  carried  in-packets,  and  cannot 
be  placed  in  the  magazine  without  them.   The  packet  there- 
fore becomes  a  necessary  part  of  the  mechanism,  just  as  the 
magazine  in  the  Lee  gun. 

GENERAL  PRINCIPLES  OF  THE  CAL.  .30  MAGAZINE. — The 
magazine  of  the  cal.  .30  remedies  the  last  two  defects. 

In  this  gun  the  magazine  is  a  fixed  box,  but,  instead  of 
projecting  vertically  below  the  receiver,  it  is  partly  hori- 
zontal and  partly  inclined  at  the  left  side,  where  it  opens 
into  the  receiver.  This  gives  a  solid  bottom  to  the  receiver, 
so  that  no  inconvenience  results  from  using  the  gun  as  a 
single-loader,  and  the  cartridges  may  be  inserted  into  the 
magazine  either  singly  by  hand  or  quickly  from  a  packet 
carrying  five  cartridges.  This  latter  arrangement  is  called 
a  quick-loader,  and  is  used  in  many  other  box-magazine  guns, 
in  which  the  packet  does  not  form  an  essential  part  of  the 
mechanism,  as  with  the  Lee,  and  the  Lee-Speed  or  English 
gun. 

333.  Description  of  the  Magazine  for  the  Cal.  .30. 

This  magazine  is  situated  under  the  receiver,  in  front  of 
the  trigger-guard  and  in  rear  of  the  barrel.  It  consists, 
Figs.  332  and  333,  of  the  horizontal  part  m  (see  also  Fig.  313) 
and  the  curved  part  O. 

The  horizontal  part  is  in  one  piece  with  the  receiver, 
and  the  curved  part  is  formed  by  the  separate  piece  O,  of 
the  proper  shape,  secured  to  the  left  side  of  the  receiver. 

The  opening  #',  through  which  the  cartridges  pass  to  the 
receiver,  is  narrowed  at  the  rear  (see  Fig.  313)  correspond- 
ing to  the  folding  down  of  the  sides  of  the  magazines  in  the 


578 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


Lee  and  Mannlicher,  and  for  the  same  purpose — that  is,  to 
hold  the  cartridges  in  the   magazine,  against  the  action  of 


M 


FIG.  332. 


FIG.  333. 


the  carrier-lever  and  spring;  and  as  with  other  box. 
magazines,  the  cartridge  must  be  pushed  forward  by  the 
bolt,  beyond  this  narrow  part,  before  it  can  rise  into  the 
receiver.  The  bottom  of  the  receiver  at  z  is  left  solid,  with 
the  advantages  noted. 


FIG.  335. 


The  cartridges  are  pushed  to  the  left,  and  into  the  re- 
ceiver, by  the  carrier-lever  N,  Figs.  334  and  335.  This  lever 
has  a  spindle,  a,  and  lug,  e,  at  its  forward  end  and  below, 
against  which  rests  a  flat  bow-spring,  S.  This  spring  5  is 
carried  in  a  small  recess,  r,  below  the  receiver  (see  also  Figs. 
332  and  333).  The  rear  end  of  5  bears  against  the  side  of 
this  recess,  r,  the  front  end  against  the  lug  e  on  the  carrier- 
lever,  and  against  the  back  of  the  spring  rests  the  lower 
edge,  5,  of  the  gate  M  which  opens  and  closes  the  mouth  of 
the  magazine. 

The  spring  5  is  thus  under  constant  compression,  due  to 
the  action  of  the  gate,  and  it  forces  the  carrier-lever  to  the 


REPEATING    OR  MAGAZINE  ARMS. 


579 


left  in  the  magazine.  When  the  gate  is  opened,  as  in  Fig. 
332,  a  lug,  //,  attached  to  it,  Figs.  334,  335,  presses  against  the 
carrier-lever  and  forces  it  to  the  right  against  the  action  of 
the  spring  5,  thus  leaving  the  magazine  clear  for  loading. 
The  spring  5  acts  also  to  keep  the  gate  M  open  or  closed, 
just  as  the  fiat  spring  on  the  rear  sight  keeps  the  sight-leaf 
up  or  downk 

The  gate  M,  Fig.  334,  has  a  thumb-piece,  /,  by  which  it  is 
opened  and  closed,  and  it  is  assembled  to  the  side  of  the 
receiver  by  the  pin  P,  Figs.  332  and  333.  The  cut-off  is 
shown  at  c,  same  figure. 

ACTION  OF  MECHANISM. — To  fill  the  magazine  the  gate 
M  is  opened  by  the  thumb-piece  t,  and  the  five  cartridges 
inserted  by  hand  singly,  or  all  at  once  from  a  quick-loader, 
the  carrier-lever  N  being  held  back  as  explained. 

When  the  gate  is  closed  the  carrier-lever  comes  into 
action,  and  forces  the  cartridges  to  the  left  and  upward. 
The  first  four  cartridges,  by  their  shape,  act  to  push  each 
other  upward  as  soon  as  they  reach  the  curved  part  of  the 
receiver.  The  fifth  cartridge  is  pushed  upward  by  the 
shape  of  the  upper  side  of  the  follower-lever.  If  the  cut-off 


K 


D      G 


FIG.  336. 


€  is  used,  it  projects  as  explained  into  the  opening  sf  of  the 
magazine,  Fig.  333,  and  forces  the  upper  cartridge  down 
sufficiently  far  to  be  out  of  the  way  of  the  bolt. 

The  assembled  mechanism  of  the  cal.  .30  rifle  is  shown  in 
the  firing  position  in  Fig.  336. 


580  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

334.  Revolvers— Classification— Conditions  to  be  fulfilled  by  a  Good 
Service  Revolver— Remarks. 

CLASSIFICATION. — The  revolver  is  a  weapon  for  personal 
defence  at  short  distances,  not  exceeding  50  or  60  yards,  and 
is  employed  principally  by  mounted  troops  and  by  officers. 

They  are  divided  into  three  classes : 

1.  Single-action  revolvers,  or  those  which  must  be  cocked 
by  hand  before  each  fire. 

2.  Self-cocking  revolvers,  in  which  by  pulling  the  trigger 
the  cocking  and  firing  are  accomplished,  till  all  the  chambers 
are  emptied. 

3.  Double-action  revolvers,  which  act  as  single-action  or 
as  self-cocking  at  the  will  of  the  firer. 

CONDITIONS  TO  BE  FULFILLED  BY  A  GOOD  SERVICE 
REVOLVER. —  i.  Its  mechanism  should  be  simple,  strong, 
easy  to  dismount  and  assemble,  and  interchangeable. 

2.  Each  chamber  which  is  to  be  fired  should  stop  exactly 
in  the  prolongation  of  the  barrel. 

3.  The  mechanism  should  work  well  whether  the  revol- 
ver be  fired  rapidly  or  slowly ;  this  rapid  or  slow  fire  being 
readily  employed  at  will. 

4.  The  bullet  should  possess  sufficient  energy  to  stop  a 
man  at  50  or  60  yards. 

5.  It  should  be  easy  to  load,  and  the  empty  cases  should 
be  readily  extracted. 

REMARKS. — The  principal  points  with  reference  to  the 
working  of  a  revolver  are,  to  insure  the  stoppage  of  rota- 
tion of  the  cylinder  in  the  proper  position,  to  obtain  rapidity 
of  fire  when  needed  and  slow  fire  at  other  times,  and  to  be 
able  to  load  and  extract  easily. 

The  stoppage  of  rotation  of  the  cylinder  at  the  proper 
time  has  been  successfully  accomplished.  The  rapid  and 
slow  firing  at  will  requires  a  revolver  of  the  third  class,  or 
a  double-action  revolver.  The  single-action  revolver  gives 
the  slow  fire,  but  will  not  fire  rapidly,  while  the  self-cocking 
revolver,  although  giving  a  rapid  fire,  does  not  give  an  ac- 
curate slow  fire,  because  of  the  prolonged  pull  upon  the 
trigger,  which  is  apt  to  derange  the  aim.  The  loading  and 
extraction  are  readily  accomplished  in  the  service  revolver, 


A  MM  UNI  TION.  5  8 1 

all  the  empty  cases  being  ejected  automatically  at  the  same 
instant,  and  the  chambers  can  be  loaded  from  a  quick-loader. 
The  condition  of  certainly  stopping  a  man  at  50  yards  has 
caused  the  retention  of  larger  calibres  for  the  revolver  than 
for  the  rifle,  those  of  the  revolver  being  0.38  and  0.45  inch. 
The  revolvers  adopted  for  the  U.  S.  service  are  the  Colt's 
double-action  cal.  .38  and  the  cal.  .45.  The  mechanism  of  the 
revolver  is  best  explained  from  a  model. 


AMMUNITION. 

335.  History — Advantages    and  Disadvantages    of  Metallic   Car- 
tridge-cases— Folded-head  Cartridges. 

HISTORY. — Small  arms  were  originally  loaded  by  pour- 
ing in  the  powder  and  then  inserting  the  ball,  each  of  these 
being  carried  separately  and  loose. 

The  powder-charge  was  next  wrapped  in  paper,  and 
hence  the  name  cartridges,  from  charta,  paper ;  later  the 
powder  and  ball  were  united  in  one  package,  and  the  opera- 
tion of  loading  was  preceded  by  the  tearing  open  of  the 
paper  containing  the  powder,  pouring  it  into  the  barrel, 
and  then  inserting  the  ball.  These  arrangements  were  used 
with  muzzle-loaders,  and  continued  up  to  the  Civil  War. 

With  the  introduction  of  breech-loaders,  a  change  in  the 
cartridge  became  necessary.  The  gas  from  the  powder 
escaped  through  the  opening  of  the  breech,  occasioning 
loss  of  force,  and  it  also  clogged  the  firing  mechanism. 

To  obviate  the  defect  of  the  escape  of  gas  through  the 
•opening  of  the  breech,  various  devices  were  provided,  such 
as  the  De  Bange  pad  in  the  French  Chassepot  rifle,  a  rubber 
packing-ring,  etc.  These  devices  prevented  the  escape  in 
the  direction  indicated  as  long  as  they  were  uninjured  by 
the  gas,  but  did  not  prevent  it  from  penetrating  into  the 
firing  mechanism,  which  was  soon  clogged. 

To  avoid  the  expense  of  manufacture,  and  the  increase  of 
weight,  which  the  use  of  the  metallic  case  entailed,  and  also 
to  avoid  the  difficulties  of  extraction,  combustible  cartridge- 
cases  were  used  with  the  early  breech-loaders. 


582  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

But  the  objections  already  stated  caused  them  to  be 
abandoned  and  led  to  the  adoption  of  the  metallic  case. 

ADVANTAGES  AND  DISADVANTAGES  OF  THE  METALLIC 
CASE. — The  metallic  case  presents  the  following  advan- 
tages :  the  escape  of  gas  is  entirely  prevented  ;  the  powder 
is  well  protected  against  shock  and  moisture;  the  compo 
nents  of  the  cartridge — powder,  primer,  and  bullet— are 
complete  and  invariable ;  the  dimensions  of  the  cartridge- 
case  are  exact,  and  there  is  no  difficulty  in  loading. 

The  disadvantages  are,  the  increase  of  weight  of  the 
cartridge  and  the  expense  of  fabrication.  The  first  is 
greatly  reduced  by  the  use  of  smokeless  powder  and  the 
reduction  of  calibre,  and  the  second  by  improved  processes 
of  manufacture,  by  which  all  the  parts  are  rapidly  and 
cheaply  made  by  machinery. 

FOLDED-HEAD  CARTRIDGES. — The  earliest  metallic  car- 
tridges were  made  of  copper,  with  a  folded  head  (Fig.  337), 

the  fulminate  by  which  the  charge 
was  fired  being  contained  in  the 
fold  a. 

These    ar,e    called    rim  -  fire    car- 
tridges.   The  objections  to  them  are  : 
i.  The   fulminate   is   exposed    to 
shocks,  which  may  cause  accidental 

FIG   "\vi 

discharge  in  handling. 

2.  The  charge  of  fulminate  is  larger  than  necessary  to 
produce  discharge,  and  hence  tends  to  rupture  the  head  of 
the  shell  at  the  fold. 

3.  The  fulminate  is  not  evenly  distributed  ;  and  as  the 
firing  was  produced  by  a  blow  of  the  hammer  on  the  rim, 
if  this  blow  fell  where  there  was  no  composition  a  miss-fire 
would  result. 

4.  The  head  of  the  case  is  not  supported  by  the  walls  of 
the  chamber  b  at  the  fold,  and  hence,  due  to  this  cause  and 
to  the  excess  of  fulminate,  the  head  was  liable  to  shear  off. 

The  principal  advantage  is  that,  as  it  was  generally  used 
in  arms  with  tubular  magazines,  there  was  little  danger  of 
explosion  by  the  shock  of  firing,  since  the  point  of  the  bullet 
did  not  rest  against  the  primer  in  the  magazine. 


AMMUNITION. 


336.  Folded-head  Cup-anvil  Cartridge — Solid-head  Cartridge. 

FOLDED-HEAD  CUP-ANVIL  CARTRIDGE. — To  remedy  the 
shearing  of  the  head  of  the  cartridge,  due  to  non-support 
by  the  walls  of  the  chamber,  and 
also  the  defects  of  the  rim  fire,  the 
folded-head  cup-anvil  cartridge,  with 
the  fulminate  at  the  centre  of  the 
head,  was  devised.  Cartridges  with 
central  primers  are  called  centre-fire 
cartridges. 

This  cartridge  is  shown  in  Fig. 
338.  In  order  to  prevent  the  action 
of  the  gas  upon  the  fold  a,  a  gas- 
check  cup  b  was  inserted  in  the  head 
of  the  case.  When  the  gas  ex- 
panded, its  pressure  was  exerted  FIG.  338. 
upon  the  cup,  and  the  fold  a  protected. 

In  the  rim-fire  cartridge,  the  blow  of  the  hammer  upon 
the  fold  of  the  head  was  resisted  by  the  wall  of  the  chamber, 
which  thus  prevented  the  fold  from  yielding,  and  the  effect 
of  the  blow  was  transmitted  to  the  fulminate.  In  this  case 
the  wall  of  the  chamber  acted  as  an  anvil. 

When  the  fulminate  was  placed  at  the  centre  of  the  head 
it  was  necessary  to  provide  an  anvil  as  before,  to  resist  the 
blow  of  the  firing-pin,  and  this  anvil  was  furnished  by  the 
cup,  b.  As  this  cup  performed  both  functions,  as  above  ex- 
plained, it  was  called  a  cup  anvil.  The  anvil  is  a  common 
feature  of  all  primers,  and  is  necessary  for  the  reason  stated. 

The  cup  anvil  was  held  in  place  by  two  crimps,  c,  in  the 
case.  The  fulminate  is  at*/,  and  ee  are  the  two  vents  through 
the  cup  anvil,  by  which  the  flame  from  the  fulminate  escapes 
to  the  charge,  the  fulminate  being  fired  by  the  blow  from 
the  firing-pin. 

The  copper  of  which  the  folded-head  cup-anvil  cartridge 
is  made  is  objectionable,  as  it  is  too  soft,  and  the  extractor 
frequently  cuts  through  it  and  fails  to  withdraw  the  case, 
and  also,  owing  to  its  lack  of  elasticity,  it  is  apt  to  stick  in 
the  chamber  after  firing.  For  these  reasons  brass  is  prefer- 


584 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


-d 


able,  as  it  is  harder  and  more  elastic,  but  owing  to  its 
hardness  the  head  cannot  be  folded. 

SOLID-HEAD  CARTRIDGES. — For  these  and  other  reasons 
the   folded-head   cup-anvil   cartridge   of  copper  was  aban- 
doned,  and    the    solid  -  head   brass 
cartridge  adopted  in  its  place. 

In  this  cartridge  (Fig.  339)  the 
head  is  formed  by  pressure,  causing 
the  metal  to  flow  into  the  shape 
shown. 

The  danger  of  shearing  at  the 
head  is  avoided,  since  the  bottom  of 
the  case,  a,  inside,  is  in  front  of  the 
shearing  plane,  b. 

The  primer  is  inserted  from  the 
outside  in  a  pocket,  c,  in  the  base  of 
the  cartridge,  and  consists  of  the 
cup  d,  the  fulminate  e,  and  the  anvil  /.  The  anvil  is  made 
of  copper,  and  has  a  cut,  g,  across  the  bottom,  and  two  ver- 
tical holes,  h,  at  the  sides,  communicating  with  g,  through 
which  the  flame  from  the  fulminate  passes  to  the  charge  by 
the  vent  i  in  the  primer  pocket. 

The  principal  defect  of  this  cartridge  is  that  its  walls  are 
thinner  in  front  than  in  rear,  and  when  the  cartridge  is 
fired  the  front  part  expands  more  than  that  in  rear,  and  is 
liable  to  stick.  Hence  if  there  is  any  movement  of  the  case  to 
the  rear,  it  is  apt  to  tear  apart. 

337.  Components  of  the  Cartridge — The  Bullet— The  Powder. 

THE  BULLET.— For  the  older  arms  the  bullet  was  made 
of  pure  lead  cast  in  a  mold.  As  improvements  were  made, 
the  soft  lead  was  found  to  shear  in  the  grooves  and  cause 
"  leading." 

Hence  the  lead  was  hardened  by  alloying  it  with  some 
other  metal,  such  as  tin  or  antimony.  The  Springfield  bullet 
is  an  alloy  of  lead  and  tin.  With  the  introduction  of  small 
calibres,  high  velocities,  and  rapid  twist,  the  hardened  lead 
did  not  present  sufficient  resistance  to  shearing,  and  the 


AMMUNITION. 


585 


jacketed  bullet  was  adopted.  The  jacket  at  present  used  is 
cupro-nickelled  steel. 

The  casting  of  the  bullet  also  was  objectionable,  since  the 
density  was  not  uniform,  and  the  centre  of  gravity  fre- 
quently did  not  coincide  with  the  longer  axis,  giving  rise  to 
irregularity  in  flight.  For  this  reason  the  bullet  was  formed 
by  compression  between  dies,  and  more  uniform  density 
thus  obtained.  In  the  Springfield  bullet  (Fig.  340)  three 
grooves  or  cannelures  are  formed  at  the  rear  end,  and  these 
are  filled  with  vegetable  wax  for  lubrication  of  the  bore. 
With  the  cal.  .30  bullet  (Fig.  341)  it  is  found  that  these  are 
not  necessary,  and  they  have  been  abandoned. 

The  shape  of  the  bullet  is  cylindro-ogival  for  the  Spring- 
field and  cai.  .30.  The  two  bullets  are  shown  (Figs.  340  and 
341).  The  weights  are:  Springfield,  500  grains;  cal.  .30,220 
grains. 


FIG.  340. 


FIG.  341. 


FIG.  342. 


Recent  experiments  have  been  made  with  a  tubular  steel 
bullet,  the  Krnka-Hebler. 

This  bullet  (Fig.  342)  is  made  entirely  of  steel  except  the 
narrow  copper  rotating  band,  a,  around  the  middle.  On 


586  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

the  rear  end  is  a  sabot,  b,  made  of  vulcanized  fibre  and 
weighing  only  a  few  grains  ;  its  object  being  to  receive  the 
pressure  of  the  powder-gas  over  a  greater  extent  of  surface, 
and  to  act  as  a  gas-check,  preventing  the  escape  of  gas 
along  the  sides  of  the  projectile.  When  the  projectile  leaves 
the  bore,  the  pressure  of  the  air  upon  the  front  surface  of 
the  sabot  causes  it  to  drop  off.  The  central  hole  allows  the 
air  to  pass  through  freely  in  flight,  and  thus  diminishes  the 
retardation  owing  to  the  decreased  surface  presented.  An 
initial  velocity  of  3000  ft.-secs.  has  been  obtained  with  this 
projectile,  with  a  pressure  of  46,000  Ibs.  per  square  inch  in 
the  gun. 

THE  POWDER.  —  Small-arms  powder  is  used  in  the 
Springfield  rifle,  weight  70  grains.  It  is  measured  auto- 
matically in  a  loading-machine,  and  after  insertion  in  the 
case  is  slightly  compressed  before  the  bullet  is  put  in.  The 
charge  of  smokeless  powder  varies  from  32  to  43  grains,  37 
of  Wetteren  or  43  of  Peyton  powder  being  at  present  used. 
As  it  is  important  with  smokeless  powders  to  secure  the 
same  amount  for  each  charge  in  order  to  regulate  the 
pressure,  these  charges  are  weighed,  and  to  insure  greater 
regularity  the  powder  is  sieved  before  loading. 

338.  Components  of  the  Cartridge— The  Case— The  Primer. 

THE  CASE. — The  general  features  of  the  cartridge-case 
have  already  been  described.  The  rim  is  for  the  purpose 
of  extraction,  limits  the  forward  motion  of  the  cartridge  in 

loading,  and  fixes  its  position  in  the 
chamber.  In  certain  box  magazines 
the  rim  occasions  some  difficulty  if 
care  is  not  exercised  in  placing  the 
cartridge  in  the  magazine.  For  ex- 
FIG.  343.""  ample,  in  Fig.  343,  if  the  cartridges 

occupy  the  position  there  shown,  it 
is  evident  that  the  top  cartridge  is  held  by  the  rim  of  the 
one  next  below,  and  consequently  the  bolt  cannot  without 
difficulty  push  it  out  of  the  magazine.  To  remedy  this  it 
has  been  proposed  to  make  rimless  cartridges,  as  in  Fig.  344, 
the  notch  a  being  for  the  purpose  of  extraction.  The  ob- 


AMMUNITION. 


587 


r\ 


r\ 


jections  to  these  cartridges  are  that  their  position  in  the 
chamber  is  regulated  by  the  bearing  of  the  shoulder  b  against 
a  corresponding  shoulder  in  the  forward  part  of  the  cham- 
ber, and  as  it  is  impossible  to  make  the  length  cd  exactly 
the  same  for  all  cartridges  and  all  chambers, 
short  cartridge  will  have  too  much  play, 
and  the  head  of  the  case,  moving  to  the  rear 
on  firing,  while  the  front  sticks  in  the  cham- 
ber, for  the  reasons  already  explained,  will 
cause  rupture  of  the  case  and  fouling  of  the 
mechanism.  In  addition,  the  operation  of 
the  extractor  is  not  always  certain. 

The  case  of  the  cal.  .30  cartridge  is  made  d— 
bottle-shaped  to  reduce  its  length  as  much  as 
possible  in  order  to  give  a  longer  path  for 
the  gas  to  work  over  and  to  diminish  wave 
action,  and  the  exterior  is  conical  to  facilitate 
f~^  extraction  in  both 
the  Springfield 
and  the  cal.  .30. 

The  contact  of 
the  old  nitrate 
powders  with  the 
brass  case  caused  FrG-  344- 

deterioration  of  the  latter,  and  it 
was  tinned  to  prevent  this. 

The  effect  of  the  new  smoke- 
less powders  on  the  case  is  not 
known,  but  the  cases  are  tinned 
as  with  the  old  powders. 

THE    PRIMER. — Its  composi- 
tion has  already  been  explained. 
With  the  new  smokeless  pow- 
ders some  difficulty  has  occurred 
in   igniting  the  charge,  and  the 
strength  of  the  primer  has  been 
increased,  with  successful  results 
primer  is,  for  safety,  sunken  be- 
The  old  Spring- 


FIG.  345. 


FIG.  346. 


as  regards  ignition.     The 

low  the  level  of  the  head  of  the  cartridge. 


588  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

field  cartridge  can  be  reloaded  ;  the  new  smokeless-powder 
cartridge  cannot  be,  except  at  the  arsenals,  on  account  of  the 
danger  from  excessive  crimping,  and  the  high  pressures 
that  result  from  an  error  in  weight  of  charge,  or  from  in- 
serting the  bullet  too  far  into  the  case,  and  also  because  of 
difficulty  in  providing  reloading-tools  for  the  small  calibre. 

The  complete  cartridges  for  the  Springfield  and  the  cal. 
,30  rifles  are  shown  in  Figs.  345  and  346. 


CHAPTER  X. 
MACHINE  AND  RAPID-FIRE  GUNS. 

MACHINE   GUNS. 

339,  Definition —  Object  —  Advantages — Disadvantages — Require- 
ments— Kinds  of  Machine  Guns 

DEFINITION. — A  machine  gun  is  one  that  is  loaded  and 
fired  by  machinery. 

OBJECT. — Its  object  is  to  deliver  a  rapid  and  continuous 
fire,  and  thereby  enable  a  few  men  to  produce  the  same 
effect  as  a  larger  number  armed  with  the  ordinary  rifle. 

ADVANTAGES. — Owing  to  the  great  volume  of  fire  deliv- 
ered by  them,  they  may  be  employed  at  decisive  moments  of 
the  attack,  and  to  defend  defiles,  ditches  of  permanent  works, 
and  for  their  moral  effect  against  mobs  and  in  street-fight- 
ing. In  the  Naval  Service  they  are  mounted  in  the  tops,  to 
sweep  the  enemy's  decks,  drive  the  cannoneers  from  their 
guns,  and  to  repel  boarders. 

DISADVANTAGES. — These  guns  are  mounted  on  wheeled 
carriages,  and  transported  like  artillery.  They  therefore 
appear  naturally  to  belong  to  that  arm  of  the  service.  But 
as  they  generally  fire  small-arm  ammunition,  they  are  unable 
to  cope  with  field-artillery  at  the  fighting  range  of  the  latter. 

This  limits  the  use  of  machine  guns  in  the  attack  to  the 
infantry  arm,  and  it  is  generally  considered  that  for  pur- 
poses of  attack  they  are  inferior  to  infantry,  as  they  do  not 
possess  its  mobility. 

For  defence  the  guns  are  very  useful  in  holding  positions 
where  they  may  be  permanently  mounted,  and  fired  in  a 
fixed  direction. 

REQUIREMENTS.— In  order  that  a  machine  gun  may  fulfil 
its  functions,  it  should,  when  once  pointed  in  a  given  direc- 

589 


590  TEXT-BOOK'  OF  ORDNANCE  AND    GUNNERY. 

tion,  retain  that  direction  unchanged  by  the  shock  of  firing; 
which  requires  that  there  shall  be  no  recoil,  and  that  the 
mechanical  operations  of  loading  and  firing  shall  not  inter- 
fere with  the  aim  or  working  of  the  gun.  These  conditions 
are  very  difficult  to  fulfil,  and  are  perhaps  more  nearly  at- 
tained in  the  Maxim  automatic  gun  than  in  any  other.  The 
gun  must  also  be  capable  of  being  rapidly  directed  upon 
any  particular  object,  and  of  having  this  direction  quickly 
changed.  This  is  accomplished  in  most  of  them  by  mount- 
ing the  gun  on  a  fork  placed  upon  the  carriage,  by  which 
means  a  quick  motion  in  azimuth,  and  also  around  the  axis 
of  the  trunnions,  can  be  given. 

The  gun  must  be  managed  by  a  small  number  of  men, 
who  should  be  well  protected  by  shields  from  the  enemy's 
fire.  The  ammunition  should  in  general  be  the  same  as  that 
used  by  the  infantry,  to  avoid  complication,  and  a  large 
supply  must  be  carried  by  the  gun  in  a  condition  ready  for 
feeding,  in  order  to  insure  rapid  and  continuous  fire.  The 
mechanism  should  not  be  liable  to  jam  or  get  out  of  order 
when  the  gun  is  fired  rapidly  ;  it  should  be  simple  and  easily 
repaired,  and  the  gun  should  not  become  heated  to  such  an 
extent  as  to  interfere  with  firing. 

KINDS  OF  MACHINE  GUNS.— The  principal  machine  guns 
which  have  been  tried  in  the  United  States  are 

The  Gatling ; 

The  Gardner; 

The  Maxim; 

The  Hotchkiss  revolving  cannon. 

Of  these,  the  Gatling  and  Hotchkiss  revolving  cannon  have 
been  adopted  for  service. 

340.  The  Gatling  Gun— Parts— Barrels— Cylinders—Casing. 

PARTS.— The  gun  consists,  Fig.  347,  of  a  number  of  breech- 
loading  rifled  barrels,  B,  usually  ten,  placed  around  and  par- 
allel to  a  central  shaft,  S.  These  barrels  are  held  in  place 
by  two  barrel-plates,  P,  P,  called  respectively  the  front  and 
rear  barrel-plates.  The  barrel-plates  are  circular  disks  as- 
sembled to  the  central  shaft  6",  and  having  holes  in  them 


MACHINE   GUNS. 


59! 


through  which  the  barrels  pass.  The  barrels  and  central 
shaft  thus  form  a  cylinder,  of  which  the  barrels  are  the  ele- 
ments and  the  central  shaft  the  axis. 

In  rear  of  the  barrels  is  the  carrier-block  C,  which  is  a 
metal  cylinder  attached  to  the  central  shaft  S.  On  the  sur- 
face of  this  cylinder  are  grooves  forming  extensions  of  the 
barrels.  These  grooves  receive  the  cartridges  from  the 


feed,  and  guide  them  while  they  are  being  pushed  into  the 
barrels  by  the  bolts,  and  they  also  guide  the  empty  shells 
while  they  are  being  withdrawn  from  the  barrels  after  firing. 

The  outer  edges  of  these  grooves  have  projections  which 
act  to  feed  the  cartridges,  as  will  be  explained. 

In  rear  of  the  carrier-block  is  the  lock-cylinder  L,  a 
second  metal  cylinder  attached  to  the  central  shaft  5,  the 
surface  of  which  forms  guides  in  which  slide  backward  and 
forward,  the  bolts  by  which  the  breech  is  opened  and  closed, 
and  the  cartridges  fired. 

On  the  rear  end  of  the  central  shaft  is  a  worm-gear,  Gy 
in  which  works  a  worm,  W,  on  the  transverse  crank-shaft  Sf. 
By  attaching  the  crank  K  directly  to  the  rear  end  of  the 
central  shaft  S,  a  rapid  fire  is  obtained  ;  when  attached  as 
shown,  the  fire  is  comparatively  slow. 

CASING. — The  central  shaft,  with  barrels  and  mechanism, 
is  mounted  in  a  frame,  the  mechanism  being  covered  by  a 
bronze  casing  which  protects  it  from  dust.  The  shaft  5  is 
journalled  in  this  frame  and  casing  in  front  and  rear,  so  that 
the  shaft,  barrels,  carrier-block,  and  lock-cylinder  revolve 
independently  of  them. 


592  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

The  trunnions  are  attached  to  the  exterior  of  the  frame, 
and  the  gun  is  mounted  on  a  fork  attached  to  the  carriage. 

The  fork  has  a  motion  in  azimuth,  and  hence  the  direc- 
tion may  be  quickly  changed  without  moving  the  carriage 
as  before  explained. 


341.  The  Gatling  Gun— Parts 
tion  of  Mechanism. 


-The  Bolts— The  Cam-groove — AC- 


FIG.  348. 


THE  BOLTS. — There  is  one  bolt  for  each  barrel.  Each 
bolt  consists,  Fig.  348,  of  a  hollow  cylinder,  through  which 
passes  the  firing-pin  #,  surrounded  by  its  spiral  main  spring, 
b.  The  firing-pin  terminates  in  rear  in  a  head,  b' ,  which  is 
used  in  cocking  and  firing.  Each  bolt  has  a  lug,  c,  project- 
ing from  its  rear  end.  This  lug  fits  into  a  groove  in  the 
casing,  and  is  the  means  by  which  the  forward  and  back- 
ward motion  is  communicated  to  the  bolts  during  the  rota- 
tion of  the  barrels.  Each  bolt  acts  with  reference  to  its  own 
barrel,  like  the  bolt  in  the  cal.  .30  rifle,  opening,  closing,  and 
locking  the  breech.  The  extractor,  d,  engages  over  the 
rim  of  the  cartridge  before  firing,  and  by  the  backward 
motion  of  the  bolt  extracts  the  empty  case  from  its  barrel. 
e  is  the  guide-rib  which  fits  in  a  corresponding  groove  in 
the  lock-cylinder,  and  guides  the  bolt  in  its  forward-and- 
back  motion. 

THE  CAM-GROOVE.— The  rear  part  of  the  cylindrical 
bronze  casing  surrounding  the  lock-cylinder  contains  a 
groove,  called  the  cam-groove,  which  may  be  regarded  as 
formed  by  the  intersection  of  the  interior  of  the  cylindrical 
casing  by  a  plane,  cd,  oblique  to  the  axis,  as  in  Fig.  349. 

This  gives  an  ellipse,  the  upper  and  lower  ends  of  which, 


MACHINE   GUNS.  593 

at  c  and  d,  are  cut  off  by  two  planes  perpendicular  to  the 

axis  of  the  cylinder.     Hence         ^ ^>  i  a 

the  sides  cd  of  the  groove 
are  arcs  of  an  ellipse,  and  the 
ends  a  and  £,  arcs  of  circles, 
with  their  planes  perpendic- 
ular to  the  axis  of  the  cylin- 
der.  The  arc  b  is  at  a  dis-  FlG-  349- 

tance  in  rear  of  the  barrels  equal  to  the  length  of  a  bolt, 
and  the  arc  a  at  a  distance  equal  to  the  length  of  the  bolt 
plus  that  of  the  cartridge,  with  a  small  allowance  for  play 
added. 

ACTION  OF  THE  MECHANISM. — When  the  crank  K,  Fig. 
347,  is  rotated,  it  causes  the  central  shaft,  with  the  barrels, 
carrier-block,  and  lock-cylinder,  to  rotate  in  the  casing. 

The  bolts,  being  held  by  the  guides  in  the  surface  of  the 
lock-cylinder,  also  rotate  with  the  barrels  and  other  parts. 
But  by  the  bearing  of  the  lugs  c,  Fig.  348,  of  the  bolts,  in 
the  elliptical  groove  cd,  Fig.  349,  in  the  breech-casing,  the 
bolts  on  the  right-hand  side  are  forced  to  move  forward 
toward  the  barrels,  and  those  on  the  left  to  move  back- 
ward. 

Fig.  350  shows  a  development  of  the  cam-groove,  barrels, 
and  firing  mechanism;  cd  being  the  development  of  the 
right-hand  side  of  the  elliptical  groove  cd,  Fig.  349,  and  c'd' 
that  of  the  left-hand  side  of  the  same  groove,  while  cc'  and 
dd'  are  the  developments  of  the  circular  arcs  b  and  a,  Fig. 
349,  respectively. 

When  the  lugs  c  of  the  bolts,  Fig.  348,  in  this  rotation, 
reach  the  part  dd' ,  called  the  "  loading  flat,"  the  cartridges 
drop  from  the  feed  into  the  grooves  in  the  carrier-block,  in 
front  of  the  bolts ;  as  the  rotation  continues,  each  right- 
hand  bolt  is  forced  forward  by  the  inclined  groove  cd, 
pushing  its  cartridge  into  the  barrel.  When  the  cartridge 
is  completely  inserted,  the  lug  c  of  its  bolt  has  reached  the 
part  cc' ,  called  the  "  firing-flat,"  and  the  bolt  thus  closes  the 
barrel,  just  as  the  bolt  of  the  cal.  .30  rifle. 

While  the  bolts  are  thus  moving  forward,  a  groove  R  on 
the  right-hand  side  of  the  casing,  catches  the  head  of  the 


594 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY, 


firing-pin  and  retains  it,  thus  compressing  the  spiral  main 
spring  and  cocking  the  firing  pin. 

This  groove  R  is  called  the  cocking-rib,  and  is  essentially 
a  short  arc  of  a  circle  whose  plane  is  parallel  to  those  of  ccf 
and  dd'.  This  arc  ends  abruptly,  so  that  when  the  firing-pin 


FIG.  350. 

is  cocked  and  the  barrel  closed,  as  in  the  figure,  a  continua- 
tion of  the  rotation  causes  the  head  of  the  firing-pin  to 
pass  out  of  the  cocking-rib.  The  firing-pin  then  moves  for- 
ward under  the  action  of  the  spiral  main  spring  and  fires 
the  cartridge.  The  rotation  still  continuing,  the  bolts  are 
withdrawn  by  the  left-hand  groove  c'd',  and  as  they  move 
back,  the  empty  cases  are  drawn  out  by  the  extractors  on 
the  bolts. 

342.  The  Gatling  Gun— Feeds— Tin  Feed-case— Objections— Bruce 
Feed— Objections. 

FEED.— The  feed   is  the  method   of  supplying  the  car- 


MACHINE   GUNS. 


595 


tridges  to  the  gun.  Various  feeds  have  been  used  with  the 
Gatling  gun,  and  changes  have  been  made  in  them  to  cor- 
rect defects  as  they  developed. 

TIN  FEED-CASE. — The  first  feed  consisted  of  a  tin  case, 

A,  Fig.  351,  of  trapezoidal  cross-section,  con-     | } 

taining  40  cartridges. 

The  cartridges  were  placed  horizontally 
in  this  case,  lying  one  above  the  other,  and 
were  held  in  the  case  by  a  spring,  s,  at  the 
lower  end,  the  upper  end  being  closed. 

A  weight,  w,  at  the  upper  end  rested 
on  the  column  of  cartridges,  and  was  provided 
with  a  projecting  thumb-piece,  /,  the  whole 
sliding  along  the  case  in  a  groove,  £-,  cut  in  the 
side.  When  in  use,  the  lower  end  was  placed 
in  an  opening  over  the  carrier-block,  the  case 
being  in  a  vertical  plane,  and  the  spring  s 
which  closed  the  lower  end  being  forced 
aside  by  the  operation  of  inserting  it. 

The    cartridges    then    fell    of   their  own 
weight  into  the  grooves  in  the  carrier-block, 
and  were  pushed  forward  by  the  bolts.     The 
sliding  weight  w,  and  thumb-piece  /,  were  intended  to  aid 
the  fall  of  the  cartridges,  especially  at  high  angles  of  eleva- 
tion. 

OBJECTIONS. — The  objections  to  this  feed  were,  that  it 
did  not  work  regularly  for  different  angles  of  elevation, 
since  the  component  of  gravity  parallel  to  the  case  varied 
with  the  angle  of  elevation.  Also,  the  cartridges  did  not 
always  fall  parallel  to  the  guide-grooves,  and  hence  jam- 
ming was  liable  to  occur,  and  in  very  rapid  firing  the  car- 
tridges did  not  fall  quickly  enough  to  supply  the  barrels. 
For  these  reasons  a  second  feed  was  introduced. 

THE  BRUCE  FEED.— This  is  a  gravity  feed,  but  is  in- 
tended to  force  the  cartridges  to  fall  parallel  to  the  guide- 
grooves  and  hence  avoid  jamming.  It  consists,  Fig.  352, 
of  an  upright  bronze  standard,  a,  to  which  is  pivoted  a 
swinging  piece,  by  having  two  grooves  in  it.  Below  the 
grooves  is  a  fixed  mouth,  £,  and  below  this  a  wheel,  d,  turn- 


FIG.  351. 


596 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


ing  freely  on  its  axis.  When  in  use  the  feed  is  inserted  in 
an  opening  in  the  breech-casing  directly  over  the  carrier- 
block  e.  The  paper  box  containing  the  cartridges,  the 

top  being  removed,  is  placed  in 
the  fixed  standard  a,  with  the  heads 
of  the  cartridges  to  the  rear.  The 
heads  of  the  cartridges  engage  in 
the  grooves  of  the  swinging-piece 
b,  and  the  paper  box  may  then  be 
pulled  off.  In  the  position  shown  in 
the  figure,  the  left-hand  column  of 
cartridges  passes  at  once  directly 
into  the  fixed  mouth  c,  and  as  each 
cartridge  strikes  the  wheel  d,  its 
weight  causes  the  latter  to  revolve 
and  present  a  new  groove  for  the 
reception  of  a  cartridge.  The  car- 
tridges thus  delivered  to  the  wheel 
d  are  in  turn  carried  round  by  it 
and  deposited  in  the  grooves  in  the 
carrier-block  e  in  the  proper  position. 
As  soon  as  the  left-hand  column  of 
cartridges  is  exhausted,  the  weight 
of  the  right  hand  column  causes  the 
swinging-piece  b  to  rotate  to  the  left, 
and  thus  brings  the  right-hand  col- 
umn over  the  fixed  mouth  c.  This 
operation  is  repeated  as  long  as  the 
supply  'of  cartridges  is  kept  up. 

OBJECTIONS.— This  feed  delivers 
the  cartridges  parallel  to  the  barrels, 
and  thus  avoids  jamming ;   but  as  it 
depends    on    gravity,   its    action    is 
variable  for  different  angles  of  eleva- 
tion, as  with  the  old  tin  case,  and  this  objection  has  been 
overcome  by  the  introduction  of  the  Accles  feed-drum. 


MACHINE   GUNS. 


597 


343.  The  Gatling  Gun— The  Accles  Feed— Advantages  and  Objec- 
tions. 

This  feed  consists  (Fig.  353)  of  a  drum,  with  two  heads 
of  brass,  connected  by  a  sheet-brass  casing.  The  distance 
apart  of  the  two  heads  is  equal  to  the  length  of  a  cartridge. 


FIG.  353. 

The  inside  of  each  head  is  grooved  in  a  spiral  form,  the 
spiral  beginning  at  the  centre  and  ending  at  the  mouth  or 
opening  of  the  drum.  The  central  part,  a,  of  the  spiral  is 
removed,  and  its  place  occupied  by  the  axis  or  pivot  of  a 
set  of  radial  arms,  b,  which  rotate  about  this  axis.  The  car- 
tridges are  inserted  through  the  mouth  c  into  the  drum, 
the  heads  of  the  cartridges  entering  the  spiral  of  one  of  the 
drum-heads,  and  the  point  of  the  buiiet  the  corresponding 
spiral  on  the  opposite  drum-head. 

The  cartridges  thus  rest  in  the  spirals  and  between  the 
radial  arms.  When  in  use,  the  feed-drum  is  inserted  in  an 
opening  in  the  breech-casing,  directly  over  the  carrier-block 
d,  the  opening  c  of  the  drum  being  down,  and  over  the 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

grooves  of  the  block,  and  the  planes  of  its  heads  at  right 
angles  to  the  axis  of  the  barrels.  Projections,  e,  are  formed 
on  the  outer  edges  of  the  grooves  of  the  carrier-block 
which  engage  with  pins,/,  joining  the  outer  extremities  of 
the  radial  arms  of  the  drum,  like  the  teeth  of  gear-wheels. 

When  the  crank  k,  Fig.  347,  of  the  gun  is  rotated,  the 
lock-cylinder,  barrels,  etc.,  revolve,  and  the  projections  on 
the  grooves  of  the  carrier-block  cause  the  radial  arms  of 
the  drum  to  rotate.  These  arms  bearing  against  the  car- 
tridges in  the  drum  force  them  along  the  spirals  toward  the 
opening  c,  from  which  they  are  delivered  to  the  grooves 
of  the  carrier-block  parallel  to  the  latter. 

ADVANTAGES  AND  OBJECTIONS.— This  drum  feeds  the 
cartridges  without  the  aid  of  gravity  and  is  hence  a  positive 
feed,  and  is  independent  of  the  angle  of  elevation. 

As  it  is  driven  by  the  carrier-block,  it  supplies  the  car- 
tridges as  fast  as  they  are  needed,  and  thus  the  feed  is  per- 
fectly regulated  ;  and  as  the  cartridges  are  guided  by  the 
spirals,  they  are  delivered  in  the  proper  position  to  the 
carrier-block  at  all  angles  of  elevation,  and  jamming  is 
Avoided. 

The  objections  are  the  weight  of  the  drum,  and  the  ex- 
tent of  its  surface  exposed  to  hostile  fire.  A  bullet  striking 
the  drum  would  render  it  useless.  For  these  reasons  a  new 
feed  has  recently  been  introduced. 

344.  The  Gatling  Gun— Latest  Improved  Feed. 

The  latest  feed  introduced  has  a  small  surface  exposed 
to  fire,  is  independent  of  gravity,  and  can  therefore  be  used 
with  equal  facility  at  any  angle  of  elevation,  and  it  is  cheap 
and  light. 

Long  strips  of  tin  or  any  cheap  flexible  metal,  Fig.  354, 
have  tongues  or  slits,  a,  punched  in  them,  one  end  of  the 
tongue  being  left  attached  to  the  strips,  and  the  other 
separated. 

These  tongues  surround  the  cartridge  and  hold  it  in 
place  on  the  strip.  The  small  rectangular  slots  b,  are 
punched  completely  through,  and  in  these  slots  fit  the  rims 


MACHINE   GUNS. 


599 


of  the  cartridge-cases,  thus  preventing  any  side  or  longitu- 
dinal motion  of  the  cartridges  with  respect  to  each  other. 


a  a  a  a  a  a\a,a  a  a  a  a  a 


FIG.  354. 

A  hopper,  a,  Fig.  355,  is  hinged  to  the  frame  which  sup- 
ports the  gun,  just  over  the  carrier-block,  and  this  hopper 
has  an  opening,  b,  on  the  left  side  through  which  the  strips 
holding  the  cartridges  are  fed.  This  opening  is  narrow  in 
front  and  wide  in  rear,  in  order  to  prevent  the  cartridges 
being  introduced  with  the  wrong  end  to  the  front.  Below 


FIG.  355- 

the  opening  b  is  a  shelf,  cy  so  shaped  as  to  guide  the  car- 
tridges and  strips  into  the  opening.  Above  the  shelf  is  a 
flat  spring,  d,  which  presses  the  cartridge-strips  down  as 


6OO  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

they  pass  through  the  opening.  A  wedge,  e,  projects  from 
the  opposite  side  of  the  hopper  and,  acting  on  each  car- 
tridge in  turn,  forces  it  out  of  the  strip,  the  tongues  a, 
Fig.  354,  bending  downward  into  recesses  provided  for 
them.  /  is  the  carrier-block,  provided  with  projections 
which  act  like  the  teeth  of  a  wheel  upon  the  cartridges, 
forcing  the  strip  to  the  right. 

When  in  use  the  strip  containing  the  cartridges  is 
pushed  into  the  opening  b  of  the  hopper.  The  crank  is  then 
rotated,  which  causes  the  projections  on  the  grooves  of  the 
carrier-block  to  act  upon  the  cartridges,  forcing  the  strip  to 
the  right  through  the  hopper.  This  action  brings  each 
cartridge  in  succession  against  the  point  of  the  wedge  e,  and 
the  action  of  the  wedge  forces  the  cartridge  out  of  its  hold 
on  the  strip  by  bending  downwards  the  tongues  a,  Fig.  354, 
and  the  cartridge  is  deposited  in  the  groove  of  the  carrier- 
block,  the  empty  strips  passing  out  at  the  right. 

345.  The    Gardner    Gun—Parts— The    Barrels— The  Casing— The 
Bolts. 

PARTS.— The  parts  of  the  Gardner  gun  are 

The  barrels ; 

The  casing ; 

The  bolts  ; 

The  firing  and  extracting  mechanism  ; 

The  cams  ; 

The  feed-valve  and  guide. 
BARRELS.— There  are  two  barrels,  a,  Fig.  356,  which  are 


FIG.  356. 


parallel  and  have  their  axes  in  the  same  horizontal  plane. 
They  have  no  motion,  and  are  loaded  and  fired  by  the  action 
of  the  bolts  and  firing  mechanism. 


MACHINE   GUNS. 


601 


THE  CASING. — This  is  of  bronze,  the  front  part,  b,  being 
cylindrical  and  forming-  a  support  and  protection  for  the 
barrels.  Two  openings,  b't  are  made  in  the  top  and  bottom, 
to  permit  a  current  of  air  to  circulate  around  the  barrels 
and  keep  them  cool  in  firing.  The  rear  part,  <;,  of  the  casing 
is  box-shaped  and  contains  the  mechanism.  It  is  closed  at 
the  top  by  a  cover,  d,  which  is  hinged  to  the  forward  part 
of  the  casing,  and  secured  by  a  screw  on  the  neck  of  the 
,cascable,  and  may  be  raised,  thus  allowing  the  mechanism 
to  be  seen  and  readily  removed. 

THE  BOLTS. — -There  are  two  bolts  of  U  shape>  Fig.  357, 


FIG.  357. 

one  for  each  barrel.  One  side  of  the  U  has  an  arm,  a,  ex- 
tending at  right  angles  to  its  length,  and  this  arm  forms  the 
bolt  proper,  and  carries  the  firing  mechanism,  and  the  ex- 
tractor, b.  The  U-shaped  part  of  the  bolt  has  a  recess,  c,  into 
which  the  surface  of  the  driving  cam  (a,  Fig.  360)  fits,  at  a 
certain  period  of  its  rotation,  and  it  has  also  a  projection,  d, 
which  at  the  proper  period  in  the  rotation  of  the  cam,  bears 
against  its  exterior  surface.  The  sear  e,  projects  in  the  recess 
c,  and  is  acted  on  by  the  cam,  when  the  latter  enters  that 
recess.  The  bolt  as  a  whole  has  a  backward  and  forward 
motion  in  the  casing,  running  on  the  truck-wheel  /.  g  is 
the  cocking-lever,  whose  action  will  be  explained. 

346.  The    Gardner    Gun — The    Firing    Mechanism — Action — The 

Extracting  Mechanism. 

THE  FIRING  MECHANISM. — This  consists  (Fig.  358)  of  a 
hring-pin,  h\  spiral  mam  spring,  i\  cocking-lever,  g\  sear, 


6O2  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

e;  and  sear-spring,/.  The  firing-pin  has  a  collar,  k,  in  front, 
and  a  toothed  sleeve,  /,  in  rear ;  the  latter  sliding  longitudi- 
nally along  the  firing-pin.  The  firing-pin  terminates  in  rear 


FIG.  358. 

in  a  head,  m,  fixed  to  the  pin ;  n  is  the  main-spring  com- 
pressor, and  o  the  cocking-cam. 

ACTION  OF  FIRING  MECHANISM. — In  the  position  repre- 
sented in  the  figure,  the  firing-pin  is  cocked,  but  the  main- 
spring is  not  compressed.  The  head,  ;«,  of  the  firing-pin,  is 
engaged  with  the  sear,  e.  As  the  bolt  is  moved  forward  by 
the  cam,  the  cocking-lever,  g,  moves  with  it,  and  the  lower 
end  of  this  lever  bears  against  the  main-spring  compressor 
n,  thus  causing  g  to  rotate,  and  acting  by  its  teeth  on  those 
of  the  sleeve  /,  the  latter  is  forced  forward,  compressing  the 
main  spring  h,  since  the  firing-pin  is  held  by  the  sear  e. 
When  the  main  spring,  //,  is  fully  compressed,  the  cam  a, 
Fig.  360,  enters  the  recess  c,  Fig.  358,  in  the  bolt,  and  press- 
ing on  the  sear  e,  releases  it.  The  firing-pin  then  moves 
forward  through  the  sleeve,  under  the  action  of  the  main 
spring,  and  fires  the  cartridge. 

As  the  bolt  moves  backward  under  the  action  of  the 
cam,  the  lower  end  of  the  cocking-lever,  g,  bears  against  the 
cocking-cam  <?,  and  the  firing-pin,  by  the  action  of  the  teeth 
of  the  cocking-lever  on  those  of  the  sleeve,  is  lorced  to  the 
rear  till  its  head,  *#,  catches  over  the  sear. 

THE  EXTRACTING  MECHANISM.— This  consists  (Fig.  359) 
of  a  hook-shaped  extractor,  b,  on  the  end  of  the  bolt  a,  which 
rides  over  the  rim  of  the  cartridge-case  s,  as  tne  latter  is 


MACHINE   GUNS. 


603 


forced  home,  and  withdraws  the  empty  shell  as  the  bolt  moves 
backward.     The  ejectors  are  two  levers,/,  pivoted  to  the 


FIG.  359. 

sides  /  of  the  casing,  the  rear  or  bent  ends,  q,  of  which  are 
struck  by  lugs,  r,  on  the  bolts  as  they  move  backwards.  The 
cartridge-case  being  held  by  the  extractor  b,  the  end,  u,  of 
the  lever,  strikes  the  case,  disengages  it  from  the  extractor, 
and  throws  it  out  of  the  casing.  The  ejectors  also  act  as 
stops,  to  prevent  the  cartridges  from  dropping  through  the 
openings  in  rear  of  the  barrels,  when  fed  down  by  the  valve. 

347.  The  Gardner  Gun— The  Cams — The  Feed-valve  and  Guide. 


FIG.  360. 

THE  CAMS. — Motion  is  given  to  all  the  parts  by  two 
cams,  a,  Fig.  360.  These  cams  are  attached  to  three  steel 
disks,  b,  at  opposite  extremities  of  a  diameter,  and  the  whole 
caused  to  rotate  around  the  axis  c  by  the  crank  d.  As  rota- 
tion continues,  each  cam  acts  against  the  U-shaped  portion 
of  its  bolt,  pushing  it  forward,  and  holding  it  motionless 
while  firing  occurs ;  then  moving  it  backwards,  and  holding 
it  motionless  while  loading  occurs.  Firing  and  loading  take 
place  when  the  cams  are  in  prolongation  of  the  axis  of  the 


604 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


arm  of  the  bolt  carrying  the  firing-pin,  at  which  time  the 
direction  of  the  force  of  recoil  passes  through  the  axis  c  of 
the  cam-disks,  and  hence  there  is  no  tendency  to  rotate. 
The  bolts  are  motionless  for  about  \  of  a  revolution  of  the 
cams,  to  allow  for  hang-fires, 

THE  FEED-VALVE  AND  GUIDE. — The  feed  is  arranged 
as  follows:  A  vertical  bronze  guide,  g,  Fig.  361,  resembling 


FIG.  361. 

the  Bruce  guide  already  explained  lor  the  Gatling  gun, 
but  without  the  wheel,  is  fixed  to  the  casing  in  rear  of  the 
barrels,  and  holds  the  cartridges  as  previously  explained. 
Below  this  feed-guide,  the  casing  is  perforated  with  two 
holes,  for  the  passage  of  the  cartridges,  and  below  these  holes 
is  the  feed-valve,  v,  Figs.  362  and  363,  which  is  a  flat  plate 
having  two  holes  corresponding  to  those  in  the  casing. 
This  valve  slides  at  right  angles  to  the  barrels,  and  is  driven 
by  a  fork-shaped  lever,  /,  which  receives  its  motion  from 
the  bolts  d,  as  they  move  forward.  By  this  arrangement  the 
cartridges  drop  from  the  feed-guide  £-,  through  the  holes  in 


MACHINE   GUNS. 


605 


the  casing,  and  these  holes  are  alternately  opened  and  closed 
by  the  feed-valve  v,  as  it  moves  to  the  right  and  left.  When 
in  the  proper  position,  one  of  the  holes  in  the  feed-valve  v,  is 
in  prolongation  of  the  corresponding  hole  in  the  casing  the 
other  hole  being  closed,  and  the  cartridge  drops  through, 
and  is  forced  by  the  bolt  into  the  chamber.  The  hole  over 
the  other  barrel  is  then  opened,  and  a  cartridge  drops,  and 
is  forced  forward  into  that  barrel.  The  details  are  best 
explained  from  the  gun. 


FIG.  362. 


FIG.  363. 

The  assembled  mechanism  is  shown  in  Figs.  362  and  363. 
a  the  barrels,  b  the  casing,  c  the  breech-cover,  d  the  bolts, 
e  the  cams,  e'  the  disks,  v  the  feed-valve,  /  the  feed-valve 
lever,  f  the  ejectors,  h  main-spring  compressor,  i  cocking- 
cam,  g  feed,/  cocking-lever. 

348.  The   Maxim  Automatic   Machine  Gun — General  Principles — 

Action  of  Mechanism — Advantage — Parts. 
GENERAL  PRINCIPLES. — The  Maxim  automatic  machine 
gun  is  so  constructed,  that  on  firing  a  single  shot,  the  force 


606  TEXT- BOOK  OF  ORDNANCE  AND    GUNNERY. 

of  the  recoil  is  utilized  for  opening  the  breech,  extracting 
the  empty  case,  and  effecting  the  various  operations  neces- 
sary to  reload  and  again  fire  the  arm,  or  prepare  it  for 
firing ;  so  that  after  the  gun  has  been  once  fired,  all  these 
operations  are  performed  automatically,  and  the  gun  con- 
tinues firing  with  great  rapidity  so  long  as  the  trigger 
remains  pulled,  and  the  supply  of  cartridges  lasts. 

ACTION  OF  MECHANISM. — The  breech  mechanism  is  oper- 
ated by  hand  to  insert  the  first  cartridge  in  the  barrel,  and 
the  trigger  is  then  pulled.  The  pressure  of  the  powder- 
gas  on  the  breech-block,  causes  the  latter,  with  the  barrel, 
to  recoil.  During  this  recoil,  the  breech  is  opened,  the 
empty  cartridge  case  extracted,  the  firing-pin  cocked,  and 
a  loaded  cartridge  brought  into  position  to  be  thrust  into 
the  chamber.  The  energy  of  recoil  not  consumed  in  the 
above  operation  is  stored  up  in  a  spiral  spring,  which  by 
its  reaction  causes  the  barrel  to  return  to  the  firing  posi- 
tion, forces  the  loaded  cartridge  into  the  chamber,  and 
closes  the  breech.  The  moment  the  breech  is  closed,  the 
gun  is  fired  automatically,  if  the  trigger  be  held  in  the 
pulled  position.  The  rate  of  fire  is  about  660  rounds  per 
minute. 

ADVANTAGE. — The  great  advantage  of  this  gun  is,  that 
being  automatic  in  its  action,  the  aiming  is  not  interfered 
with  by  the  operation  of  a  crank  or  other  device  to  work 
the  mechanism,  and  hence  it  can  be  pointed  readilv  in  any 
direction,  and  the  direction  changed  with  great  facility. 

PARTS. — The  gun  consists  practically  of  two  parts — a 
recoiling,  and  a  non-recoiling  part.  The  recoiling  part 
embraces  the  barrel,  the  lock,  the  crank,  the  breech-block, 
and  an  inner  frame  with  guides  and  bearings,  on  which 
these  parts  move.  The  recoiling  part  may  be  considered 
the  gun  proper. 

The  non-recoiling  part  consists  of  a  casing  and  two  side 
frames,  in  which  the  recoiling  part  moves. 

349.  The  Maxim  Automatic  Machine  Gun — The  Barrel  and  Frame 
— The  Breech  Mechanism. 

THE  BARREL  AND  FRAME. — The  gun  has  a  single  barrel, 


MACHINE   GUNS. 


607 


a,  Fig.  364,  attached  to  the  inner  frame  b,  and  is  an  ordinary 
rifled  one  of  the  desired  calibre.  It 
has  bearings  at  c  and  d,  which  rest 
in  corresponding  supports  in  the 
bronze  casing,  and  on  these  bear- 
ings the  barrel  slides  back  and 
forth  in  action.  The  frame  b  is 
open  at  the  top  and  bottom,  and 
resembles  a  box.  This  frame  car- 
ries the  breech  mechanism,  and 
hence  the  latter  moves  back  and 
forth  with  the  barrel  and  frame, 
and  has  also  motion  with  respect 
to  the  frame,  as  will  be  explained. 
Near  the  rear  end  of  the  frame,  the 
crank-shaft  e  passes  through  both 
sides,  and  has  a  motion  of  rota- 
tion in  the  frame.  On  the  right 
hand  side,  this  crank-shaft  pro- 
jects, and  upon  it  is  fixed  a  bent 
lever,  ff,  of  the  shape  shown. 
On  the  left  side  of  the  frame  b 
the  crank-shaft  e  projects  also, 
and  to  it  is  attached  the  short 
crank  g.  The  strong  spiral 
spring  h  by  which  the  counter- 
recoil  is  produced,  is  attached  at 
h'  to  the  fixed  casing,  and  at  h" 
to  the  short  crank  g.  Any  rota- 
tion of  the  crank-shaft  e  in  the 
direction  of  the  arrows,  will  there- 
fore increase  the  tension  of  the 
spiral  spring  h,  which  will  be 
wound  up  around  e.  Also  any 
backward  movement  of  barrel  and 
frame,  with  reference  to  the  fixed 
casing,  will  increase  this  tension, 
since  the  spiral  spring  is  fixed  to 
the  casing  at  h' . 


FIG.  364. 


6o8 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


THE  BREECH  MECHANISM.— This  is  contained  between 
the  sides  of  the  inner  frame  b.     In  Fig.  365  let  e,  as  before, 


FIG.  365. 

represent  the  crank-shaft.  Upon  this  shaft,  and  between 
the  sides  of  the  inner  frame  b,  is  fixed  an  arm  or  crank,  iy 
so  that  any  rotation  of  e,  causes  i  to  rotate  also. 

At  the  end  of  i,  a  fork-shaped  piece  or  link,/,  is  attached 
by  an  axis,/',  and  the  front  end  of  j  is  pivoted  to  the  breech- 
block k  at  k' .  The  breech-block  is  therefore  held  between 
the  prongs  of  the  forked  link  j.  When  the  crank-shaft  e 
is  rotated  in  the  direction  of  the  arrow,  the  pivot  j'  de- 
scribes the  arc  of  a  circle  in  the  same  direction.  As  the 
breech-block  k  can  only  slide  back  and  forth  in  the  direc- 
tion of  the  arrow,  it  is  evident  that  this  rotation  of  the 
shaft  e,  as  described,  will  pull  the  breech-block  backward, 
with  reference  to  the  barrel  and  frame,  along  the  guides  m' ', 
and  at  the  same  time  the  surface  /  of  the  fork-shaped  link 
j  will  describe  the  arc  of  a  circle  around  k ',  and  will,  con- 
sequently, move  down  along  the  rear  curved  surface  of  the 
breech-block. 

350.  The  Maxim  Automatic  Machine  Gun— The  Breech-block  and 
Carrier. 

THE  BREECH-BLOCK  AND  CARRIER. — The  breech-block 
consists  of  the  part  k  (Figs.  366,  367),  which  moves  back- 


MACHINE   GUNS. 


609 


ward  and  forward  parallel  to  the  axis  of  the  barrel,  the 
bearing  mt  sliding  in  the  groove  m'  in  the  inner  frame  b ; 
and  of  the  part  n,  called  the  carrier,  which  is  attached  to 
the  front  part  of  the  breech-block  k,  and  moves  backward 
and  forward  with  it,  but  has  also  a  vertical  sliding  motion 
along  its  front.  This  carrier,  n,  extracts  the  loaded  cart- 
ridges from  the  belt  which  carries  them,  feeds  them  to  the 
barrel,  and  extracts  the  empty  case  after  firing.  Its  action 
is  as  follows:  When  in  the  firing  position  (Fig.  366)  the 


FIRING.  POSITION, 


FlG.  366. 


LOADING    POSITION. 

FIG.  367. 

forked  link  j  is  nearly  horizontal,  and  the  carrier  n  is  at 
its  extreme  upward  position.  After  firing,  when  j  rotates 
downward  (Fig.  367),  the  cam  <?,  which  is  a  part  of  j,  is  no 
longer  in  contact  with  the  second  cam  <?',  pivoted  to  k,  and 
working  n.  The  carrier  n  is  then  held  up  by  two  guides  on 
the  sides  of  the  inner  frame,  shown  in  Fig.  371,  upon  which 
the  arms,  q,  rest,  and  is  pressed  down  as  the  block  slides. 


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TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


backward,  by  two  springs,  /,  attached  to  the  fixed  casing, 
and  acting  on  the  two  projecting  arms,  q,  on  the  carrier. 
When  the  block  moves  forward  again,  the  forked  link/  rises, 
and  the  cam  o,  acting  on  o' ,  raises  the  carrier  at  the  end  of 
the  forward  movement  of  the  block.  Two  grooves  in  the 
rear  face  of  n,  slide  on  bearings,  q ',  on  the  front  of  the  breech- 
block k.  The  front  surface  of  the  carrier  n  is  grooved,  so 
that  the  heads  of  the  cartridges  will  fit  in  it.  As  it  rises, 
these  grooves  engage  the  rirn  of  the  cartridge  in  the  cham- 
ber, and  that  of  a  second  cartridge  above  this  in  the  feed- 
belt.  When  the  piece  is  fired,  the  backward  motion  of  the 
breech-block  causes  the  carrier  n  to  draw  the  loaded  cart- 
ridge out  of  the  feed-belt,  and  the  empty  case  out  of  the 
chamber.  The  carrier  n  is  then  forced  down  by  the 
springs  /,  as  explained,  which  brings  the  loaded  cartridge 
opposite  the  chamber,  and  the  empty  shell  opposite  the  ejec- 
tor-tube. A  forward  motion  of  the  breech-block  then  de- 
posits the  cartridge  in  the  chamber,  and  ejects  the  empty  case. 
351.  The  Maxim  Automatic  Machine  Gun — The  Firing  Mechanism 
—The  Feed. 


FIG.  368. 

THE  FIRING  MECHANISM.  —  This  is  contained  in  the 
interior  of  the  breech-block  k.  It  consists  (Fig.  368)  of  the 
firing-pin  a,  the  main  spring  b,  which  acts  also  as  a  sear- 
spring,  the  tumblers,  sear  d,  salety-sear  e,  and  its  spring/. 


MACHINE   GUNS.  6ll 

The  action  is  as  follows :  When  the  forked  link  j  (see 
also  previous  figures)  moves  downward,  it  strikes  the  pro. 
jecting  end  c'  of  the  tumbler  c,  and  causes  the  latter  to 
rotate  in  the  direction  of  the  arrow.  The  upper  part  of  the 
tumbler,  bearing  in  a  notch  in  the  firing-pin  a,  draws  back 
the  latter,  compressing  the  mainspring  b,  till  the  sear  d 
catches  under  the  notch  d'  of  the  tumbler.  At  the  same 
time,  the  safety-sear  e  drops  into  a  notch  on  the  upper  side 
of  the  firing-pin  a.  If  the  firing  is  to  be  continuous,  the 
trigger-rod  g  is  kept  constantly  pulled  backward  in  the 
direction  of  the  arrow,  by  pressing  with  the  thumbs  on  the 
lever  h.  If  the  pressure  upon  h  is  relieved,  the  spring  i 
forces  the  trigger-rod  g  forward,  and  the  firing  ceases,  the 
trigger  being  no  longer  pulled. 

Supposing  the  trigger-rod  to  be  kept  pulled,  the  sear  d, 
striking  against  the  projection  on  the  trigger-rod  g  as  the 
lock  moves  forward,  is  disengaged  from  the  notch  d'  in  the 
tumbler,  and  the  firing-pin  is  held  back  by  the  safety-sear  e 
alone.  As  the  forked  link  /  rises  in  closing  the  breech,  it 
strikes  the  projecting  end  e'  of  the  safety-sear,  just  as  the 
breech  is  closed,  disengaging  e  from  its  notch  in  the  firing- 
pin,  which  then  moves  forward  and  fires  the  cartridge.  In 
this  case  the  firing  is  automatic  and  continuous. 

If  the  firing  is  to  be  by  single  shots,  the  trigger-rod  g  is 
not  kept  in  the  pulled  position.  In  this  case  the  forked  link/ 
rises  and  disengages  the  safety  sear  et  as  before.  The  firing- 
pin  is  now  held  back  only  by  the  sear  d  and  tumbler  c. 
Pulling  the  trigger-rod  disengages  d,  and  fires  the  cartridge. 

THE  FEED. — The  cartridges  are  contained  in  belts,  made 
by  uniting  two  strips  of  canvas,  with  intervals  between  them 
to  hold  the  former.  These  belts,  with  their  cartridges,  are 
contained  in  a  box  placed  below  the  gun.  Over  the  rear 
end  of  the  barrel  is  a  box-shaped  feed  attached  to  the  casing 
(Fig.  369). 

This  feed  contains  a  slide,  a,  having  a  pin,  b,  acted  on  by 
a  lever,  c.  The  slide  has  two  spring-pawls,  d\  and  two 
other  spring-pawls,  e,  are  fixed  to  the  feed-box,  but  not 
attached  to  the  slide.  The  belt  containing  the  cartridges 
is  passed  into  the  feed-box,  till  the  first  cartridge  is  caught 


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TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


by  the  spring-pawls  d.  As  the  barrel  recoils,  a  projection 
on  the  inner  movable  frame,  strikes  the  lower  end  of  the 
lever  at  cf,  and  causes  the  slide  a  to  move  to  the  left,  by  the 
action  of  this  lever  on  the  pin  b.  The  spring-pawls  d,  mov- 
ing with  the  slide  a,  push  the  cartridges  and  the  belt  to  the 
left,  till  a  cartridge  is  in  position  to  be  caught  by  the  groove 
in  the  carrier  as  it  rises.  The  lower  spring-pawls  e,  being 
pivoted  to  the  feed-box,  do  not  slide,  and  hence  hold  the 


FIG.  369. 

belt  and  cartridges  in  place,  while  the  slide  a,  with  the  pawls 
d,  moves  back  again  to  the  right  to  engage  over  another 
cartridge,  /is  a  wooden  roller,  over  which  the  belt  passes, 
and  the  mouth  of  the  feed-box  has  guides  for  directing  the 
motion  of  the  belt.  . 

352.  The  Maxim  Automatic  Machine  Gun— Action  of  the  Mechanism. 
The  Figs.  370  and  371  show  the  assembled  gun  and  mechan- 
ism.    On  the  exterior  right  side  of  the   fixed  casing,  is  a 
curved  arm,  a,  a  stop,  b,  and  a  buffer-spring,  c. 

When  the  gun  is  fired,  supposing  the  trigger  to  remain 
pulled,  the  barrel,  inner  frame,  and  breech  mechanism  recoil 
together  for  a  short  distance. 

At  the  end  of  this  recoil  the  curved  arm  d  of  the  bent 
lever  strikes  against  the  curved  arm  a,  fixed  to  the  outer 
case.  This  causes  a  rotation  of  the  crank-shaft  e,  and,  as 
previously  explained,  the  breech-block  k  is  drawn  back  from 
the  chamber,  thus  opening  the  breech,  and  at  the  same 


MACHINE   GUNS. 


613 


time  drawing  a  loaded  cartridge  out  of  the  belt,  and  ex- 
tracting the  empty  case  from  the  chamber.  As  long  as  the 
rotation  of  the  crank-shaft  e  continues,  the  breech-block  k 
moves  backward. 

During  the  last  part  of  its  motion,  the  carrier  n  is  forced 
downward  by  the  springs  /,  Fig.  371,  and  thus  the  loaded 


FIG.  370. 


FIG.  371. 

cartridge  is  brought  in  line  with  the  chamber,  and  the  empty 
case  with  the  ejector-tube  r. 

During  this  time  also,  the  firing-pin  has  been  cocked, 
and  the  strong  spiral  spring  /extended  by  this  rotation  of 
the  crank-shaft  e,  as  explained.  The  rotation  of  the  crank- 
shaft e  continues,  till  the  outer  arm  g  of  the  bent  lever, 
strikes  the  buffer-spring  c,  fixed  to  the  casing.  The  re- 
action of  this  spring,  and  the  tension  of  the  spiral  spring/, 
now  cause  the  crank-shaft  e  to  rotate  in  the  opposite 
direction,  and  the  spiral  spring /also  forces  the  barrel  and 
frame  forward. 


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TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


As  the  rotation  of  e  continues,  the  breech-block  k  moves- 
forward,  the  loaded  cartridge  is  thrust  into  the  barrel,  and 
the  empty  shell  out  through  the  ejector-tube  r.  As  the 
breech  closes,  the  carrier  n  rises,  and  grasps  another  cart- 
ridge which  has  been  fed  forward  by  the  slide  s  in  the  feed- 
box,  as  explained,  and  when  the  breech  is  completely  closed 
the  forked  link  j  strikes  the  safety  sear  e' ,  and  fires  the 
cartridge. 

The  barrel  is  surrounded  by  a  bronze  casing,  z,  which  is 
filled  with  water  for  keeping  the  barrel  cool  during  the 
rapid  firing,  and  a  provision  is  made  for  the  escape  of  the 
steam  if  the  water  is  heated  to  the  boiling-point. 

353.  The  Hotchkiss  Revolving  Cannon — General  Features — Rotating 
Mechanism — Loading  Mechanism — Extracting  Mechanism 
— Action. 

GENERAL  FEATURES.  —  This  machine  gun  differs  from 
the  others  in  its  weight  and  calibre,  being  much  heavier, 
and  firing  a  projectile  weighing  about  one  pound,  which 
may  be  either  shell  or  canister.  It  resembles  in  some  re- 
spects the  Gatling  gun,  already  described,  and  is  composed 
of  a  group  of  five  barrels  assembled  around  a  central  shaft, 
the  whole  revolving  in  front  of  a  heavy  breech,  which  con- 
tains all  the  mechanism.  It  differs  from  the  Gatling  gun  in 
having  only  one  loading,  one  firing,  and  one  extracting 
apparatus  for  the  five  barrels. 


FIG.  372. 

ROTATING  MECHANISM.  —  This  consists  (Fig.  372)  of  a 
cam- wheel,  a,  operated  by  a  crank,  and  working  against  a. 
series  of  studs,  b,  on  the  rear  end  of  the  central  shaft  c. 

This  cam-wheel  is  mounted  in  a  recess  in  the  breech, 


MACHINE   GUNS.  615 

and  its  peculiar  feature  is  that  the  grooves  </,  in  its  surface, 
are  partly  screw-threads,  and  partly  planes  at  right  angles 
to  the  axis  of  the  cam-wheel  shaft.  The  object  of  this 
arrangement  will  be  explained. 

LOADING  MECHANISM.  —  On  the  left  side  of  the  solid 
breech  is  situated  a  loading  piston.  This  moves  back  and 
forward  in  a  recess,  parallel  to  the  axis  of  the  barrels.  The 
piston  itself  (b,  Fig.  373)  is  cylindrical,  and  has  an  arm,  a, 
which  is  flat,  and  carries  a  toothed  rack. 


a' 


FIG.  373.  FIG.  374. 

EXTRACTING  MECHANISM. — The  extractor  is  also  situated 
in  a  recess  on  the  left  side  of  the  breech,  and  below  and  par- 
allel to  the  loading-piston.  Its  shape  is  shown  in  Fig.  374, 
the  front  end  carrying  a  hook-shaped  extractor,  the  rear 
end  having  an  arm  with  a  slot,  a,  and  the  upper  edge  form- 
ing a  toothed  rack. 

ACTION  OF  LOADING  AND  EXTRACTING  MECHANISM. — 
When  the  cam-wheel  is  rotated  by  the  crank,  if  the  spiral 
part  of  its  grooves,  d,  Fig.  372,  is  bearing  against  one  of 
the  studs,  b,  the  central  shaft  and  barrels  rotate.  If,  how- 
ever, the  plane  grooves  act  against  these  studs,  the  barrels 
do  not  move,  and  are  held  in  position  by  the  binding  of 
these  plane  surfaces  against  the  studs. 

In  Fig.  375,  a  represents  the  axis  of  the  cam-wheel,  b 
and  c  the  loading-piston  and  extractor  respectively,  in  their 
relative  positions  when  assembled. 

The  crank  d  is  attached  to  the  axis  a,  and  the  toothed 
wheel  e  is  mounted  on  an  independent  axis  on  the  left  side 
of  the  breech,  gearing  into  b  and  c.  When  the  axis  a  rotates, 
a  pin,^-,  on  the  end  of  the  crank  d,  engaging  in  the  slot/,  at 


6l6  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

the  end  of  the  extractor-arm,  draws  back  the  extractor. 
This  occurs  while  the  plane  grooves  of  the  cam-wheel  are 
bearing  against  the  studs  on  the  central  shaft,  and,  conse- 
quently, there  is  no  rotation  of  the  barrels. 


FIG.  375. 

As  the  extractor  moves  backward,  it  withdraws  the 
empty  case  from  the  barrel  last  fired.  By  the  backward 
motion  of  the  extractor,  the  wheel  e  is  caused  to  rotate,  and, 
acting  on  the  rack  of  the  loading-piston,  it  causes  the  latter 
to  move  forward,  thus  pushing  the  loaded  cartridge  in  front 
of  it  into  the  chamber.  The  loading  and  extracting  are 
performed  while  the  barrels  stand  still.  As  the  rotation  of 
the  cam-wheel  still  continues,  the  pin  g  in  the  slot  f  reaches 
a  part  of  this  slot  which  is  concentric  with  a.  At  this  time 
the  extractor  and  loading-piston  stand  still,  while  the  barrels 
rotate. 

Continued  rotation  of  the  cam-wheel  beyond  this  point 
of  rest,  reverses  the  motion  of  the  loading-piston  and  ex- 
tractor, pushing  the  latter  forward,  and  drawing  the  former 
backward,  and  so  on. 

354.  The  Hotchkiss  Revolving  Cannon —  The  Feed  — The  Firing 
Mechanism. 

THE  FEED.— The  cartridges  are  contained  in  zinc  or  tin 
cases — ten  in  a  case.  These  cases  are  inserted  in  a  feed- 
tray,  a,  Fig.  376,  mounted  on  the  left  side  of  the  breech ; 
the  act  of  inserting  the  case  causing  it  to  open  and  allow 
the  cartridges  to  enter  the  tray.  Resting  against  the  top 
of  the  loading-piston  b,  is  a  hinged  lid,  c,  attached  to  the 


MACHINE   GUNS. 


6i7 


breech.  As  the  loading-piston  moves  forward,  pushing  the 
cartridge  in  front  of  it  into  the  barrel,  this  hinged  lid  pre- 
vents the  entrance  of  a  second  cartridge.  When  the  load- 
ing-piston moves  back  in  rear  of  the  lid,  the  latter  drops 


FIG.  376. 

down  by  its  own  weight  and  that  of  the  cartridges  resting 
against  it,  and  allows  a  fresh  cartridge  to  drop  in  front  of 
the  loading-piston.  The  piston  immediately  moves  forward, 
raising  the  lid,  and  keeping  back  the  other  cartridges. 


FIG.  377. 

THE  FIRING  MECHANISM. — This  is  arranged  as  follows, 
(Fig.  377) :  On  the  right  hand  lower  side  of  the  breech  is 
a  strong  firing-pin,  a,  moving  in  a  recess,  and  acted  on  by 
the  main  spring  b.  On  the  shaft  of  the  cam-wheel  is  a  spiral 
cam,  c,  which  is  cut  off  abruptly  at  d.  The  arm  e  of  the 
firing-pin,  bears  against  this  spiral  cam,  and  the  pin  is  con- 


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TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


stantly  pressed  forward  by  the  main  spring.  As  the  cam- 
wheel  rotates,  the  spiral  cam,  acting  on  the  arm  e,  grad- 
ually draws  back  the  firing-pin,  compressing  the  mainspring 
b.  When  this  spring  is  compressed  to  its  full  extent,  the 
spiral  ends  abruptly  at  d,  and  at  this  time  the  barrels  are 
standing  still.  The  firing-pin  then  moves  forward,  driven 
by  the  main  spring,  and  fires  the  cartridge.  Hence  the 
loading,  firing,  and  extraction  in  this  gun  are  performed 
while  the  barrels  are  stationary.  The  recoil  is  borne  by 
the  heavy  breech,  which  is  made  of  cast-iron,  and  is  recessed 
to  receive  the  various  parts  of  the  mechanism. 


FIG.  378. 

These  parts  are  strong  and  not  liable  to  break,  and  are 
readily  accessible  for  repair.  The  various  parts  assembled 
are  shown  in  Fig.  378. 


RAPID-FIRE   GUNS.  619 


RAPID-FIRE  GUNS. 

355.  Characteristics  of  Rapid-fire  Guns— Object— History. 

CHARACTERISTICS.  —  A  rapid-fire  gun  is  distinguished 
from  a  machine  gun  by  having  a  larger  calibre,  loading  by 
hand,  having  generally  one  barrel,  and  an  artificial  means 
of  checking  recoil  and  returning  the  gun  to  the  firing  posi- 
tion. It  uses  metallic  ammunition,  and  rapidity  of  fire  is 
obtained  by  the  use  of  a  simple  breech  mechanism,  which 
works  quickly,  cocking  the  firing-pin,  and  extracting  the 
empty  case,  in  the  act  of  opening. 

OBJECT. — The  object  of  rapid-fire  guns  is  to  defend  naval 
vessels  against  the  attack  of  swift  torpedo  boats,  by  deliver- 
ing a  rapid  and  easily  directed  fire  of  projectiles  having 
sufficient  energy  to  penetrate  the  plates  of  these  boats ;  and 
also  for  piercing  the  lighter-armored  parts  of  large  ships. 
In  the  land  service  their  use  is  not  so  well  defined.  In 
order  to  utilize  the  rapid  fire  of  which  they  are  capable,  it 
is  necessary  that  the  aim  shall  be  maintained  upon  a  given 
object,  and  not  altered  by  the  recoil  of  piece  or  carriage. 
In  the  naval  service,  owing  to  the  character  of  the  mount- 
ing, this  object  is  very  readily  attained,  the  gun  being 
mounted  on  an  elastic  or  spring-return  carriage,  fixed  to 
the  vessel,  by  which  arrangement  the  gun  is  brought  back 
to  the  firing  position  after  discharge  without  derangement 
of  the  aim.  In  the  land  service  similar  mountings  have  been 
provided,  attached  to  wheel-carriages,  but  in  general  the 
shock  of  recoil  alters  the  direction  of  the  piece,  due  to  the 
mobility  of  the  carnage,  and  hence  it  must  be  redirected 
after  each  fire.  In  the  latest  mounting  for  the  land  service, 
spring-return  devices  have  been  abandoned,  and  a  rigid 
carnage  adopted.  This  carriage  is  provided  with  a  spade 
at  the  end  of  the  trail,  which  is  forced  into  the  ground  by 
the  recoil,  and,  when  fixed,  holds  the  gun  and  carriage  in 
place. 

HISTORY.  —  The  Hotchkiss  revolving  cannon,  already 
described,  was  first  used  when  torpedo  boats  were  adopted,, 


62O 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


but  it  was  found  impossible  to  give  sufficient  velocity  to  the 
projectiles  from  this  gun  to  pierce  their  plates,  or  to  increase 
the  calibre  much  beyond  1.75  inches,  owing  to  the  great 
weight  of  the  group  of  barrels.  Under  these  circumstances 
Hotchkiss  invented  a  single-barrelled  rapid-fire  gun,  with  a 
sliding  breech-block,  using  metallic  ammunition,  and  firing 
a  much  heavier  projectile  than  the  revolving  cannon,  with  a 
muzzle-velocity  of  1800  ft-seconds.  From  this  time  these 
guns  have  rapidly  developed  in  power,  and  many  different 
systems  of  breech-closing  have  been  devised. 

The  principal  systems  are  the  Hotchkiss,  Nordenfelt, 
Driggs-Schroeder,  Maxim,  Gruson,  Krupp,  and  Armstrong, 
and  a  few  of  these  will  be  described  as  types. 

356.  The  Hotchkiss  Rapid-fire  Gun— The  Gun— The  Breech 
Mechanism  —  Action. 

THE  GUN. — The  body  of  the  gun  consists  of  a  tube  and 
a  jacket,  united  by  shrinkage. 

The  jacket  extends  to  the  rear  of  the  tube,  and  is  slotted 
vertically  to  receive  the  breech  block. 


X 

? 

y 

, 

c 

d 

LEFT    SIDE. 

FIG.  379. 

^BREECH  MECHANISM.— The  breech  mechanism  consists 
(Flg-  379)  of  a  wedge-shaped  block,  which  rises  and  falls  in 
a  vertical  direction  in  the  slot  at  the  rear  end  of  the  jacket, 
instead  of  moving  horizontally,  as  in  the  Krupp.  Its  front 
surface,  a,  is  perpendicular  to  the  axis  of  the  bore,  and  its 


RAPID-FIRE   GUNS.  621 

rear  surface,  b ',  is  inclined  to  that  axis,  so  that  the  block,  in 
rising,  gradually  moves  forward  towards  the  barrel,  cc  are 
guide-grooves  parallel  to  the  rear  face  b' ,  and  correspond- 
ing projections  in  the  breech-slot  fit  into  these  grooves,  and 
guide  the  block  in  its  motion.  On  the  left  side  of  the 
block  is  the  stop-groove  d.  A  bolt  passes  through  the  left 
side  of  the  breech,  and  entering  this  groove,  prevents  the 
block  from  falling  out  of  its  recess  when  the  breech  is 
opened.  In  front  of  this  groove,  and  on  the  same  side  of 
the  block,  is  the  extractor-groove  e.  The  extractor  is 
exactly  similar  to  that  already  described  in  the  Hotchkiss 
mountain  gun,  except  that  it  works  in  a  recess  on  the  left 
side  of  the  breech,  instead  of  on  the  top.  Its  lug  bears  in 
the  groove  e,  and  as  the  block  falls,  the  extractor  is  moved 
back  very  slowly  at  first,  extracting  the  empty  case  from  the 
chamber,  and  then  very  quickly,  owing  to  the  sudden 
change  of  form  of  the  groove  e,  ejecting  the  case  from  the 
gun.  On  the  right-hand  side  of  the  block  is  a  groove,  /, 
called  the  stud  way.  A  crank-shaft,  g,  passes  through  the 
right-hand  side  of  the  breech,  projecting  into  the  breech 
slot,  and  to  this  inner  projection  is  attached  the  crank  h> 
with  a  stud,  //,  at  its  extremity,  working  in  the  groove  or 
studway  /.  The  crank-shaft  g  is  operated  by  two  handles, 
i,  attached  to  it  on  the  outside. 

ACTION. — When  the  crank-shaft  g  is  turned  by  the 
handles  i  in  the  direction  of  the  arrow,  the  stud  h'  moves 
at  first  in  a  part  of  the  groove  /,  concentric  with  g,  and 
hence  no  motion  of  the  block  occurs.  During  this  time  the 
hammer  is  cocked,  as  will  be  explained. 

The  stud  h'  now  enters  the  eccentric  part  of  the  groove 
/,  and  causes  the  block  to  descend.  As  soon  as  it  is  started, 
it  will  fall  by  its  own  weight,  till  arrested  by  the  stop-bolt 
bearing  against  the  top  of  the  stop-groove  d.  A  reversal  of 
the  rotation  of  the  crank-shaft  g,  after  loading,  causes  the 
block  to  rise,  and  the  block  in  rising,  forces  the  projectile 
home. 

The  opening  of  the  breech-block  in  firing  is  prevented 
as  follows :  When  the  breech  is  closed,  the  weight  of  the 
block  is  supported  by  the  stud  //'.  At  this  time  the  vertical 


622 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


plane  through  the  centre  of  h'  is  in  front  of  that  through  the 
centre  of  the  crank-shaft^.  Hence  the  weight  of  the  block 
acting  vertically  tends  to  keep  the  latter  closed. 

357.  The  Hotchkiss   Rapid-fire   Gun— Firing  Mechanism — Action 
— Remarks. 

FIRING  MECHANISM. — The  firing  mechanism  (Fig.  380) 
is  contained  in  recesses  in  the  front  portion  of  the  block,  and 
consists  of  a  hammer,  a,  mounted  on  a  rocking-shaft  b  (see 
also  Fig.  379),  a  main  spring,  c,  a  sear,  d,  and  a  sear-spring,  e. 

The  rocking-shaft  b  passes  through  the  lower  front  cor- 
ner of  the  breech-block,  and  projects  beyond  the  right  side, 
carrying  on  its  right  extremity,  a  curved  arm  or  cam,  k,  Fig. 
379,  called  the  cocking-toe.  The  crank-shaft  g,  which  is 


fixed  to  the  breech  (Fig.  379),  carries  a  cam,  /,  called  the 
cocking-cam,  which  is  just  above  k. 

ACTION.— When  the  handles,  i,  Fig.  379,  are  rotated  in 
the  direction  of  the  arrow,  the  cam/ comes  in  contact  with 
the  cocking-toe  k,  on  the  rocking-shaft  b,  Figs.  379  and  380, 
drawing  back  the  hammer  a,  and  compressing  the  main- 
spring c.  At  this  time  there  is  no  motion  of  the  breech- 
block, because  the  stud  h' ,  Fig.  379,  is  moving  in  the  con- 
centric part  of  its  studway, /,  as  explained. 

The  rotation  of  the  handles,  t,  continues,  till  the  hammer 
a  is  cocked,  the  sear  d  catching  in  a  notch  on  the  rocking- 


RAPID-FIRE    GUNS.  623 

shaft  b,  the  block  all  the  while  remaining  motionless.  As 
soon  as  the  cocking  is  accomplished,  the  breech-block  falls 
and  opens  the  breech.  The  end  of  the  sear  d  projects  be- 
yond the  rear  surface  of  the  breech-block,  and  when  the 
latter  is  home,  the  sear  is  in  contact  with  the  trigger  t,  and, 
pulling  it,  fires  the  charge.  The  piece  cannot  be  fired  be- 
fore the  breech  is  closed,  ist,  because  the  firing-pin  of  the 
hammer  is  not  opposite  the  primer  ;  2d,  the  trigger  will  not 
touch  the  sear;  3d,  the  cam/ on  the  shaft  g  will  catch  the 
cocking-toe  k  before  the  firing-pin  can  reach  the  primer. 

The  main  spring  e  is  so  connected  with  the  rocking- 
shaft  b,  on  which  the  hammer  is  mounted,  that  its  lower  leaf 
acts  downward  and  its  upper  leaf  upward,  and  hence  the 
pressure  and  friction  of  the  rocking-shaft  in  its  bearings  are 
very  much  diminished. 

REMARKS. — All  parts  of  the  mechanism  are  readily  ac- 
cessible and  easily  dismounted.  For  aiming,  a  stock,  a,  Fig. 
381,  is  bolted  to  the  left  side  of  the  piece  if  the  gun  is  on  a 


FIG.  381. 

rigid  carriage,  or  to  the  left  side  of  the  carriage  if  the  gun 
recoils.  This  stock  has  handles,  b,  for  grasping  with  the 
left  hand  at  different  elevations,  and  a  rubber  tube,  c,  against 
which  the  left  shoulder  rests  in  firing.  For  the  naval  ser- 
vice the  gun  is  generally  mounted  with  its  trunnions  resting 
in  a  fork.  This  fork  turns  in  azimuth  in  a  heavy  socket,  and 
this,  combined  with  the  vertical  motion  of  the  gun  around 
the  axis  of  the  trunnions  gives  a  motion  in  any  direction. 


624 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


358.  The  Nordenfelt  Rapid-fire  Gun— The  Breech  Mechanism- 
Action. 

THE  BREECH  MECHANISM. — The  breech  mechanism  in 
this  system  combines  the  sliding  and  rotating  motions,  so  as. 
to  avoid  guillotining  the  cartridge  in  forcing  it  home. 

The  breech-block  (Figs.  382,  383,  and  384)  consists  of  two 
parts,  the  first  part,  or  block  proper,  B,  and  the  rear  part,  or 
wedge,  W.  The  front  part  B  rotates  around  the  shaft  S, 
which  passes  through  the  breech,  while  the  rear  part  or 
wedge,  W,  has  at  first  a  vertical  downward  sliding  motion 
along  the  back  of  B,  till  it  reaches  the  position  shown  in 
Fig.  383,  the  two  upper  surfaces  r  r,  then  forming  one  con- 
tinuous cylindrical  surface,  at  which  time  both  parts  rotate 
backward  together  around  the  shaft  5,  Fig.  384.  C  is  a 


--E 


P' 


FIG.  382. 


FIG.  383. 


FIG.  384- 


cam,  fastened  upon  the  shaft  5,  and  having  a  slot  in  it,  in 
which  the  pin  P,  attached  to  the  wedge,  works.  E  is  the 
extractor  and  ejector. 

ACTION.— A  lever-handle  is  attached  to  the  right  extrem- 
ity of  the  shaft  5,  outside  the  breech.  After  firing,  the 
parts  of  the  block  are  in  the  position  shown  in  Fig.  382.  As 
the  lever-handle  on  the  shaft  5  is  rotated,  it  causes  the  cam 
C  attached  to  5  to  rotate  downwards.  The  slot  in  the  cam, 
bearing  on  the  pin  P,  forces  the  wedge  W  downwards,  till 
it  stands  in  the  position  shown  in  Fig.  383.  The  pin  P  is 
now>at  the  end  of  the  slot  in  the  cam  6",  and  a  continuation 
of  the  rotation  of  the  lever-handle  and  shaft  5,  causes  both 


parts  of  the  block  to  rotate  together  to  the  rear,  opening  the 
breech  (Fig.  384).  At  the  beginning  of  this  rotation,  the 
extractor  E  is  moved  slowly  backward,  withdrawing  the 
empty  case.  This  motion  afterwards  becomes  more  rapid, 
ejecting  the  case  from  the  gun. 

After  the  loaded  cartridge  is  inserted  in  the  gun,  the 
rotation  of  the  lever  on  the  shaft  5  is  reversed.  This  causes 
both  parts  of  the  block  to  rotate  to  the  front,  till  the  front 
part  B  comes  in  contact  with  the  breech.  The  wedge  W  is 
then  forced  vertically  upward  by  the  action  of  the  cam  C, 
till  it  occupies  the  position  shown  in  Fig.  382,  completely 
closing  the  breech.  The  parts  are  held  in  position  by  the 
pin  P,  at  the  last  moment  of  closing,  entering  a  concentric 
part  of  the  slot  in  the  cam  C,  which  supports  the  wedge  in 
position. 

359.  The  Nordenfelt  Rapid-fire   Gun— The    Firing    Mechanism- 
Action — Remarks. 

THE  FIRING  MECHANISM. — This  is  arranged  as  follows 
(Fig.  385):  The  firing-pin  a  passes  through  the  front  part, 
B,  of  the  breech-block.  In  rear,  it  has  projecting  lugs,  bt  one 


FIG.  385. 

on  each  side.     The  middle  part  of  the  sliding  wedge  W  is 
hollowed  out,  to  receive  the  parts  of  the  mechanism.     The 


UII7IRSITT 


626  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

main  spring  c  is  secured  at  one  end  against  the  rear  face 
of  the  block  B,  while  the  other  end  bears  against  the  rear 
faces  of  the  lugs  b,  of  the  firing-pin  a,  and  urges  the  latter 
forward. 

Two  wedge-shaped  lugs  d,  on  the  sliding  part  W  of 
the  block,  one  of  which  is  shown,  act  upon  the  lugs  b  to 
cock  the  firing-pin,  when  the  sliding  part  of  the  block 
descends. 

The  sear  e  works  on  a  pivot,  e\  resting  against  the  rear 
face  of  the  front  part  of  the  block,  and  catches  under  the 
head  of  the  firing-pin  as  shown,  when  the  latter  is  cocked. 
Its  lower  end  projects  beyond  the  rear  face  of  the  block, 
and  is  in  contact  with  the  trigger/ when  in  the  firing  posi- 
tion, g  is  a  safety  lug  on  the  wedge,  and  h  the  correspond- 
ing lug  on  the  sear,  i  is  a  tappet-trigger,  so  called,  consisting 
of  a  shaft  working  in  a  bearing  on  the  rear  face  of  the  front 
part  B  of  the  block,  and  having  upon  it  two  arms  or  cranks 
/  and  k,  set  at  an  angle  with  each  other.  There  is  also  a 
vertical  groove  on  the  front  of  the  sliding  wedge,  not  shown 
in  the  figure,  which  ends  abruptly  in  a  shoulder,  and  which 
works  the  tappet-trigger.  This  may  be  called  the  tappet- 
trigger  groove. 

ACTION. — In  the  position  shown  in  the  figure,  the  parts 
are  ready  for  firing.  On  pulling  the  trigger/,  the  firing-pin 
a  moves  forward,  under  the  action  of  the  main  spring  c,  ex- 
ploding the  cartridge.  The  lever  on  the  main  shaft  5  is 
now  rotated,  and  the  sliding  wedge  descends.  As  it  moves 
down,  the  wedge-shaped  lugs  d,  engage  in  front  of  the  pro- 
jecting lugs  b  of  the  firing-pin,  and  force  the  latter  back 
against  the  action  of  the  main  spring  c.  When  the  firing- 
pin  is  forced  back  to  its  full  extent,  the  shoulder  of  the 
tappet-trigger  groove  on  the  wedge  W,  acting  on  the  army, 
causes  the  shaft  of  the  tappet-trigger  i  to  rotate,  and  forces 
the  inner  crank-arm  k  backward  against  the  sear  e,  retaining 
the  latter  in  the  cocked  position.  The  cartridge  is  now 
inserted,  the  lever-handle  reversed,  and  the  breech  closed. 
As  the  wedge  Arises  into  its  closed  position,  the  wedge- 
shaped  lugs  d  rise  above  the  firing-pin,  and  the  projecting 
part  of  the  sear  e  comes  in  contact  with  the  trigger/.  The 


RAPID-FIRE   GUNS.  627 

firing-pin  is  now  held  back  by  the  sear  e,  which  in  turn  is 
held  by  the  arm  cf ,  of  the  main  spring  c,  bearing  on  the  lug 
e".  A  pull  on  the  trigger /depresses  the  projecting  end  of 
the  sear  e,  disengages  the  sear  from  the  firing-pin,  and  allows 
the  latter  to  move  forward  and  fire  the  cartridge. 

REMARKS. — The  cartridge  cannot  be  fired  before  the 
breech  is  completely  closed,  for  the  following  reasons  : 

ist.  While  the  wedge  is  rising,  the  lugs,  d,  are  in  front  of 
the  projections,  b,  on  the  firing- pin.  Hence,  if  the  firing- 
pin  moves  forward  at  this  time,  the  projections,  £,  will  strike 
against  the  lugs,  dt  and  prevent  the  firing-pin  from  reaching 
the  cartridge. 

2d.  The  lugs,  d,  clear  the  projections,  b,  on  the  firing- 
pin  before  the  breech  is  completely  closed.  At  this  instant, 
however,  the  safety  lug  g  on  the  wedge  comes  just  in  front 
of  the  corresponding  safety  lug  h  on  the  sear,  so  that  the 
sear  cannot  be  moved  till  the  breech  is  completely  closed, 
at  which  time  g  rises  above  h. 

360.  The  Driggs-Schroeder  Rapid-fire  Gun— The  Breech  Mechanism 
— Action. 

This  gun  is  an  American  invention,  and  its  breech  sys- 
tem combines  the  rotating  and  sliding  movements,  as  in  the 
Nordenfelt,  but  its  distinguishing  feature  is  that  the  breech- 
slot  does  not  extend  through  the  top  of  the  breech,  and  the 
block  rests  in  grooves  on  the  top  and  sides  of  this  slot. 
This  gives  greater  strength,  protects  all  the  working  parts, 
and  enables  the  weight  of  these  parts  to  be  reduced,  thereby 
facilitating  the  operations  of  opening  and  closing  the  breech. 

THE  BREECH  MECHANISM.— The  breech  mechanism  con- 
sists of  a  block,  a,  Fig.  386,  having  grooves,  b,  and  projec- 
tions, c,  cut  upon  its  top  and  sides,  which  fit  into  corre- 
sponding recesses  in  the  top  and  sides  of  the  breech  recess. 
d  is  a  shaft  passing  through  the  sides  of  the  breech,  and 
through  the  block  a,  about  which  motion  of  the  latter  takes 
place,  e  is  a  cam  attached  to  the  shaft  d,  and  rotating  with 
it ;  ff  a  surface  in  the  interior  of  the  block  of  the  shape 
shown,  which  is  in  contact  with  the  cam  e,  the  rear  part  of 


628 


TEXT-BOOK  OF  ORDNANCE   AND    GUNNERY. 


/being  inclined  backward  and  upward,  and  the  front  part/' 
being  circular  and  concentric  with  the  axis  of  d.  The  rear 
surface/  ends  in  a  cylindrical  pin,  g.  h  is  an  inclined  sur- 
face on  the  lower  rear  end  of  the  block,  against  which  the 
cam  e  acts  at  a  certain  period  of  its  rotation,  i  is  a  slot  in 


FIG.  386. 


FIG.  388 


the  breech-block,  which  allows  the  block  to  slide  in  a  direc- 
tion at  right  angles  to  the  axis  of  d.  j  is  the  extractor, 
there  being  two  of  these;  k  a  guide-bolt  screwed  through 
the  breech-casing,  and  fitting  into  the  guide-groove  /  on  the 
side  of  the  block.  There  are  two  of  these  guide-bolts,  one 
on  each  side. 

ACTION. — In  Fig.  386  the  block  is  shown  in  the  firing 
position,  in  387  in  the  partly  opened,  and  in  388  in  the  fully 
opened  position.  When  the  shaft  d  is  rotated  to  the  rear 
by  hand  after  firing,  the  toe  m  of  the  cam  e  passes  along 
the  cam  surface  ff,  permitting  the  block  to  descend. 
Should  the  block  not  drop  freely,  the  lower  face  n  of  the 
cam,  acting  on  the  inclined  surface  h,  forces  the  block 
downward,  the  slot  i  in  the  block  allowing  this  motion 
with  reference  to  the  shaft  d.  The  guide-groove  /  is  also 
so  shaped  as  to  allow  this  motion  with  reference  to  the 
guide-bolts,  k. 


RAPID-FIRE   GUNS.  629 

This  vertical  motion  of  the  block  continues  until  the 
block  has  descended  a  distance  sufficient  to  disengage  the 
projections,  c,  from  the  corresponding  recesses  in  the  top 
and  sides  of  the  breech.  The  block  is  now  resting  on  the 
toe  m  of  the  cam,  and  the  guide-bolt,  as  shown  in  Fig.  387, 
is  just  entering  the  curved  portion  of  the  guide-groove. 
The  block  now  has  a  double  movement,  downward  by  virtue 
of  the  toe  continuing  to  move  along  the  surface  ff,  and 
rotary  owing  to  the  shape  of  the  guide-grooves.  This 
motion  continues  till  the  notch  o  in  the  cam  comes  to  a  full 
bearing  against  the  cylindrical  pin  gt  when  the  block  will 
rotate  around  d  as  an  axis  till  the  breech  is  open.  As  the 
block  rotates  to  the  rear,  the  extractor-groove  q  strikes  the 
tail  p  of  the  extractor  j,  and  rotates  it  backward,  slowly 
at  first,  and  then  more  rapidly,  owing  to  the  shape  of  the 
abutting  surfaces ;  extracting  and  ejecting  the  empty  case. 
The  charge  is  now  inserted,  and  the  rotation  of  d  reversed. 
This  causes  the  block  to  rotate  around  d  till  its  projections, 
c1  are  ready  to  enter  their  recesses  in  the  breech,  the  notch 
o  of  the  cam  e,  bearing  against  the  pin  g  of  the  block. 

When  the  rotation  of  the  block  is  finished,  the  pressure 
of  the  cam  on  the  surface/,  causes  the  block  to  rise,  and  seat 
itself  in  the  recesses  in  the  breech.  The  toe  m  .of  the  cam 
then  passes  to  the  concentric  surface  f,  and  supports  the 
weight  of  the  block  during  firing  and  keeps  it  in  its  seat  in 
the  breech.  The  movement  along  the  concentric  surface/' 
is  continued  until  the  toe  m  of  the  cam  passes  over  the 
centre  of  rotation  d,  and  prevents  the  downward  thrust  of 
the  block  from  having  any  tendency  to  turn  the  cam 
backward,  and  it  is  therefore  held  rigidly  and  securely  in 
place. 


361.  The  Driggs-Schroeder   Rapid-fire  Gun — The  Firing   Mechan- 
ism— Action — Remarks. 

THE  FIRING  MECHANISM. — This  consists  (Fig.  389)  of  a 
firing-pin,  a,  working  in  a  recess  in  the  block,  and  having 
a  shoulder,  b,  in  front. 


630  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

A    strong    spiral    main    spring,    c,   bears    against    this 
shoulder,    its    rear    end    resting    against   a    corresponding 

shoulder  in  the  block,  g  is 
the  full-cock  notch  ;  h,  the 
sear,  acting  vertically  in  a  re- 
cess at  the  rear  end  of  the 
block ;  i,  the  sear-spring,  seat- 
ed in  a  recess  in  the  block, 
and  acting  against  the  lower 
end  of  the  sear  to  force  the 
latter  vertically  upward.  k 
is  a  projecting  lug  on  the 
firing-pin  a,  which  bears  in  a 
circular  recess,/,  in  the  front 
upper  surface  of  the  cam  e. 

ACTION. — When  the  cam  e 
is  rotated  to  the  rear  by  the 
shaft  d,  the  surface  of  the  cir- 
cular recess  /,  acting  against 


FIG.  389. 


the  projecting  lug  k  on  the  firing-pin,  withdraws  the  point 
of  the  latter  through  its  hole  in  the  block,  so  that  it  will 
allow  the  block  to  descend  freely.  As  the  rotation  of  the 
cam  e  continues,  the  firing-pin  is  drawn  back  still  further, 
compressing  the  spiral  main  spring  c,  till  the  firing-pin  is 
fullv  cocked,  at  which  time  the  sear  h,  acted  on  by  its 
spring  i,  rises,  and  engages  in  front  of  the  full-cock  notch 
g,  and  the  firing-pin  is  thus  retained  in  its  cocked  position. 
When  the  breech  is  closed,  the  cam  e  is  rotated  forward, 
and  the  lug  k  is  no  longer  in  contact  with  the  surface  of  the 
groove  j.  The  sear  h,  being  pulled  vertically  downward 
by  a  lanyard  attached  at/,  is  disengaged  from  the  full-cock 
notch,  and  the  firing-pin  a  moves  forward,  firing  the  car- 
tridge. 

REMARKS. — The  cartridge  cannot  be  fired  before  the 
breech  is  completely  closed,  because  until  it  is  closed  the 
groove  j  in  the  cam  e  is  in  such  a  position  as  to  catch  the 
lug  k  of  the  firing-pin  if  the  latter  should  move  forward, 
and  thus  prevent  the  firing-pin  from  striking  the  cartridge. 


RAPID-FIRE    GUNS. 


362.  The  Maxim  Semi-automatic  Rapid-fire  Gun — The  Breech  Mech- 
anism— Action. 

This  gun  differs  from  those  previously  described  in 
being-  semi-automatic ;  that  is,  the  firing  of  the  cartridge 
causes  the  barrel  and  breech  mechanism  to  recoil  together, 
opens  the  breech,  cocks  the  firing-pin,  and  thus  prepares  the 
gun  for  the  insertion  of  a  fresh  cartridge.  The  act  of  in- 
serting the  cartridge  closes  the  breech,  and  if  the  trigger  be 
kept  pulled,  fires  the  piece. 


FIG.  390. 


FIG.  391. 


THE  BREECH  MECHANISM. — This  consists  (Figs.  390  and 
391)  of  a  breech-block  a,  hollowed  out  at  b  to  receive  the 
firing  mechanism.  This  block  moves  vertically  upward  and 
downward  in  a  slot  in  the  rear  part  of  the  barrel. 

Attached  to  a  projection  on  the  lower  side  of  the  barrel 
is  the  shaft  c,  about  which  motion  of  the  breech-block  takes 
place.  Two  arms  d,  one  on  each  side,  are  attached  to  the 
shaft  c  and  rotate  with  it.  These  arms  are  connected  in 
rear  at  their  upper  ends,  by  a  pin  e,  which  passes  through 
the  breech-block  a,  and  works  in  a  slot  /  in  the  block. 
This  slot  is  at  first  concentric  with  the  axis  of  c,  and  is  after- 
wards eccentric  to  that  axis,  g  is  a  handle  attached  to  the 
shaft  c,  outside  the  gun,  for  the  purpose  of  starting  the 
mechanism,  and  can  be  readily  detached,  h  is  the  extractor 
and  ejector,  having  two  projections  z,  one  on  each  side, 
which  fit  in  corresponding  recesses/  in  the  breech-block. 
k  is  a  strong  spring,  one  end  of  which  bears  against  the  pin 


632  TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 

I  on  the  short  arm  of  the  lever  d,  and  which  presses  the 
long  arm  of  d  constantly  upward,  m  is  a  cam  fastened  to 
the  shaft  c,  and  n  is  a  catch  pivoted  to  the  jacket,  and  hav- 
ing no  motion  in  the  direction  of  recoil.  It  is  constantly 
pressed  downward  by  the  spring,  o. 

ACTION  OF  THE  BREECH  MECHANISM. — The  parts  as  rep- 
resented in  Fig.  390  are  in  the  firing  position,  the  breech 
being  closed.  Before  firing,  the  operating  handle  g  is  re- 
moved from  the  shaft  c.  When  the  piece  is  fired,  all  the 
parts  except  the  catch  n,  with  its  spring  o,  move  to  the 
rear  in  recoil,  the  barrel  sliding  in  the  jacket,  which  remains 
fixed. 

As  they  move  to  the  rear,  the  cam  m  slides  along  the 
fixed  catch  n,  till  the  projecting  corner  of  m  has  passed  be- 
yond the  end  of  n,  when  the  spring  o  forces  n  downward. 
When  the  end  of  the  recoil  is  reached,  a  strong  spring,  not 
shown  in  the  figure,  acts  to  draw  all  the  parts  back  to  their 
former  position.  As  the  parts  move  forward,  the  project- 
ing toe  or  corner  of  the  cam  m,  strikes  against  the  end  of 
the  catch  n,  and  as  the  forward  motion  of  the  parts  con- 
tinues, m  is  forced  to  rotate  backwards. 

This  causes  the  arms  d  to  rotate  downward,  carrying 
with  them  the  pin  e,  which  passes  through  the  slot/  in  the 
breech-block.  As  the  front  part  of  this  slot  is  concentric 
with  reference  to  c,  no  motion  of  the  breech-block  occurs  at 
first,  but  at  this  time  the  firing-pin  is  cocked. 

As  the  forward  motion  of  the  parts  continues,  the  toe  or 
corner  of  the  cam  m  is  freed  from  the  catch  n  by  the  up- 
ward motion  of  m,  which  strikes  against  n.  When  the  pin 
e  enters  the  eccentric  part  of  the  slot  f  the  breech-block 
descends.  In  its  descent  it  forces  the  extractor  backward, 
slowly  at  first,  and  afterwards  more  rapidly,  by  the  action  of 
the  studs  s  on  the  sides  of  the  block  which  bear  on  the  tail 
of  the  extractor.  This  downward  motion  of  the  block,  and 
backward  motion  of  the  extractor,  continues,  till  the  lugs  i 
on  the  extractor,  catch  in  the  recesses/,  of  the  block.  The 
breech  is  now  open  (Fig.  391)  and  ready  for  loading.  When 
the  long  arm  of  d  rotates  downward,  the  short  arm  moves 
upward,  and  compresses  the  spring  k.  This  spring  tends 


RAPID-FIRE   GUNS. 


633 


to  raise  the  breech-block  by  its  action  on  the  short  arm  ot 
d,  but  the  block  cannot  rise,  because  it  is  held  by  the  pro- 
jections i  of  the  extractor  bearing  in  the  recesses  j  oi  the 
block.  When  the  cartridge  is  inserted,  its  rim  strikes 
against  the  extractor,  and  frees  the  lugs  i  from  the  recesses 
j,  and  the  pressure  ol  the  spring  k  on  the  short  arm  of  the 
lever  d  causes  the  block  to  rise,  thus  completely  closing 
the  breech. 

363.  The    Maxim    Semi-automatic    Rapid-fire    Gun — The    Firing 
Mechanism — Action — Remarks. 

THE  FIRING  MECHANISM. — This  consists  (Figs.  392  and 
393)  of  a  hammer  Et  rotating  around  a  shaft  a,  which  passes 

•E 


^  A?         K          ts's 

FIG.  392.  FIG.  393. 

through  the  breech-block.  This  hammer  is  pressed  con- 
stantly lorward  by  the  main  spring  5,  the  upper  branch  of 
which  acts  against  the  lower  bent  end  e'  of  the  hammer. 
The  firing-pin  G  is  a  separate  piece,  which  is  held  in  place 


634  TEXrf-BOOK  OF  ORDNANCE   AND    GUNNERY. 

by  the  bolt  P  passing  through  a  slot  in  it,  this  slot  allowing 
the  pin  to  move  backwards  and  forwards  for  a  short  dis- 
tance. In  front,  the  firing-pin  is  acted  on  by  a  spiral  spring, 
which  forces  it  backward  as  soon  as  the  pressure  of  the 
hammer  E  is  removed.  The  sear  /  rotates  around  a  shaft 
c  in  the  breech-block,  and  is  constantly  pressed  upward  by 
the  spring  s,  which  is  a  fork  of  the  lower  branch  of  the  main 
spring  S.  The  safety-sear  C  also  rotates  around  the  same 
shaft  c,  and  is  constantly  pressed  downward  by  the  spring 
s',  which  is  also  a  fork  of  the  lower  branch  of  the  main 
spring  5.  The  hammer  E  has  two  notches  e"  and  e'" 
which  engage  in  the  corresponding  notches  i  of  the  sear  1 
and  c'  of  the  safety-sear,  C  respectively. 

The  sear  /  is  attached  to  a  lever  K,  which  is  pivoted 
around  c,  and  extends  to  the  rear,  where  it  comes  in  contact 
with  a  trigger,  T,  Fig.  393. 

ACTION  OF  FIRING  MECHANISM. — As  represented  in 
Fig.  392,  the  charge  has  just  been  fired.  When  counter- 
recoil  begins,  the  pin  e  which  passes  through  the  slot  /  in  the 
breech-block,  and  which  connects  the  upper  extremities  of 
the  arms  attached  to  the  main  shaft,  begins  to  move  along 
the  concentric  portion  of  the  groove/.  During  this  time 
there  is  no  vertical  motion  of  the  block,  as  explained,  but  the 
pin  e  strikes  against  the  lower  part,  e' ,  of  the  hammer,  and 
depresses  it,  thus  drawing  back  the  upper  part,  E,  and  com- 
pressing the  main  spring  5.  This  continues  till  the  hammer 
is  fully  cocked,  at  which  time  the  notch  e"  on  the  hammer 
E  is  in  front  of  the  corresponding  notch  i  of  the  sear  /,  and 
the  notch  e'"  on  the  hammer  is  engaged  in  the  notch  c'  of 
the  safety-sear  C.  The  hammer  is  now  held  back  by  the 
safety-sear  C,  this  latter  having  been  lowered  by  the  action 
of  the  spring  s'  till  it  is  in  front  of  the  slot  /.  As  soon  as 
the  hammer  E  is  withdrawn  from  the  firing-pin  G,  the  latter 
is  forced  back  by  its  spiral  spring,  and  the  block  is  now  free 
to  descend. 

When  the  cartridge  is  inserted  the  breech-block  rises. 

As  it  does  so,  the  pin  e  moves  up  along  the  slot  /,  and 
strikes  the  end  of  the  safety-sear  C,  which  projects  in  front 
ol  the  slot/,  and  is  therefore  in  the  path  of  the  pin  e.  This 


RAPID-FIRE   GUNS.  635 

disengages  the  notch  c'  of  the  safety-sear  from  the  notch  e'" 
ot  the  hammer  E.  The  notch  e"  of  the  hammer  E  then 
engages  with  the  notch  i  of  the  sear,  and  the  hammer  is  now 
held  back  only  by  the  sear  /.  Pulling  the  trigger  disen- 
gages the  notch  i  of  this  sear  from  the  notch  e'!  of  the  ham- 
mer, and  fires  the  piece.  If  the  trigger  be  kept  pulled,  it  is 
evident  that  the  piece  will  fire  on  the  closing  of  the  breech, 
because  the  hammer  E  is  then  held  back  only  by  the  safety- 
sear  C,  and  the  pin  e  strikes  this  safety-sear  in  closing,  as 
explained,  and  frees  its  notch  c'  from  the  notch  e'"  of  the 
hammer. 

REMARKS. — The  piece  cannot  be  fired  before  the  breech 
is  completely  closed,  ist,  because  the  firing-pin  is  not  oppo- 
site the  primer;  and  2d,  because  firing  cannot  take  place  till 
the  safety-sear  is  disengaged,  and  this  is  done  only  by  the 
act  of  closing,  and  cannot  be  accomplished  till  that  time. 

364.  Ammunition  for  Rapid-fire  Guns — Projectiles — Cases. 

The  ammunition  for  the  different  systems  of  rapid-fire 
guns  is  similar  in  almost  every  respect,  differing  only  in  the 
kinds  of  fuze  used,  each  system  having  its  own,  but  all  being 
of  the  same  type.  All  these  guns  use  metallic  ammunition. 

PROJECTILES. — The  projectiles  are  of  four  kinds  :  com- 
mon shell  (Fig.  394),  made  of  cast  iron  ;  steel  shell  (Fig.  395) ; 
shrapnel  (Fig.  396) ;  and  canister  (Fig.  397).  The  two  kinds 
of  shell  are  similar  in  construction  except  that  the  base  of 
the  steel  shell  is  an  independent  piece  screwed  in,  and  hav- 
ing its  inner  surface  concave,  so  that  it  will  tend  to  form  a 
gas-check  when  the  bursting-charge  explodes,  and  retain  the 
gases  till  they  acquire  sufficient  pressure  to  rupture  the 
walls.  The  point  of  the  steel  shell  is  made  sharp  for  armor- 
piercing,  while  that  of  the  common  shell  is  cut  off,  and  the 
two  may  always  be  distinguished  by  this  difference  in  their 
points.  The  fuzes  are  placed  in  the  base,  leaving  the  point 
and  head  solid.  Many  of  the  steel  projectiles  are  made  by 
electro-welding. 

The  shrapnel  (Fig.  396)  is  composed  of  a  body,  a  head, 
and  a  base.  The  body  is  made  of  a  steel  tube  weakened 
longitudinally  by  six  cuts,  in  order  that  it  may  rupture 


636 


TEXT-BOOK  OF  ORDNANCE  AND    GUNNERY. 


readily.     The  head  is  of  brass,  fitted  with  a   combination 
fuze,  and  the  upper  end  of  the  body  is  crimped  into  a  recess 


FlG-  398-  FIG.  399.  FIG.  400. 

in  the  head.     The  base  is  a  steel  plug  forced  into  the  body 
under  pressure,  or  screwed  in.     The  interior  is  rilled  with 


RAPID-FIXE   GUNS. 


637 


bullets,  the  layers  being  separated  by  cast-iron  disks,  as  ex- 
plained in  the  U.  S.  shrapnel  for  field-guns.  The  bursting- 
charge  is  contained  in  a  tin 'cup  in  front. 

The  case-shot  (Fig.  397)  consists  of  a  thin  sheet-brass 
case,  with  a  conical  head,  and  a  bottom  of  soft  brass  acting 
as  a  rotating  band.  The  bottom  is  strengthened  on  the 
inside  with  a  loose  plate  of  sheet  iron.  The  case  is  filled 
with  hardened  lead  balls  packed  in  sawdust. 

CASES. — These  are  of  three  kinds  : 

1.  The  solid   drawn  case  (Fig.    398),  made  as  described 
under  small-arm  ammunition. 

2.  The  built-up  case  (Fig.  399),  consisting   of   a  drawn 
tube  of  brass,  bent  inward  at  the  head,  and  furnished  with 
an  inner  and  an  outer  cup  of  brass,  which  are  riveted  to  a 
sheet-iron  disk  on  the  outside  to  strengthen  the  construction. 
In  some  cases  the  sheet-iron  disk  is  omitted,  and  the  outer 
cup  used. 

3.  The  wrapped  case  (Fig.  400),  consisting  of  a  sheet  of 
brass  of  trapezoidal  shape  wrapped  into  a  cylinder,  and  the 
head  formed  as  in  a  built-up  cartridge. 

The  latter  case  is  now  abandoned  except  for  the  Hotch- 
kiss  revolving  cannon.  All  the  cartridges  are  centre- 
primed.  The  projectile,  fuze,  charge,  and  case  are  assembled, 
forming  a  complete  cartridge,  the  only  limit  in  size  being 
the  weight  readily  handled  by  one  man.  On  this  account, 
for  the  larger  calibres  the  projectile  and  case  are  separated. 

The  assembled  cartridge  is  shown  in  Fig.  401. 


FIG.  401. 


INDEX. 


A 

PAGE 

A  and  B,  value  of 54 

Absorbents  classified,  dynamite 115 

Absorbents,  inert,  dynamite •  115 

Accles  feed 597 

Accuracy  of  fire,  increase  of 539 

Accuracy  of  guns,  comparison  of , 519 

Acid,  Emmens .....-...» ...  118 

Acid,  picric , 118 

Action  of  breech  mechanism,  seacoast  guns , 266 

Action  of  drill-press 1 74 

Action  of  gunpowder  in  a  gun , t . . . .  31 

Action  of  lathe 169 

Action  of  mechanism,  3.6-inch  mortar 249 

Action  of  milling-machine 175 

Action  of  planer 171 

Action  of  shaper 172 

Action  of  teeth 158 

Adjustments,  Le  Boulenge 93 

Advantages  of  Noble  gauge 102 

Advantages  of  reduction  of  calibre 538 

Air-packing 101 

Air-space,  initial,  reduced  length  of , 40 

a  and  ft  characteristics 55 

aand  ft,  determination  of r 67 

Ammonium  nitrate  powders   126 

Ammonium  picrate   1 18 

Ammunition-chest 413 

Ammunition  for  rapid-fire  guns 651 

Ammunition,  history  of 581 

Ammunition,  small  arm .......  581 

Amount  of  heat,  Noble  and  Abel's  experiments, 24 

Annealing  gun-forgings - 152 

639 


640  INDEX. 


Annealing  of  gun-steel I4I 

Angle  of  departure 34$ 

Angle  of  elevation 34& 

Angle  of  elevation  in  recoil •  •  ••  45 l 

Angle  of  fall , 34* 

Angle  of  inclination 378 

Angle  of  sight 347 

Angle  of  traces 4O2 

Anti-friction  washers  and  springs,  seacoast  guns 261 

Apparatus,  Letard's IO3 

Apparatus,  Noble  and  Abel's  experiments 20 

Application  of  Noble  and  Abel's  pressure  curve 38 

Arrangement  of  wires,  Le  Boulenge 87-90 

Area  of  orifice,  constant  orifice,  hydraulic  buffer 459 

Area  of  orifice,  variable  orifice,  hydraulic  buffer   4^3 

Armor 3^7 

Armor,  backing  for 32i 

Armor,  chilled  cast  iron 3T7 

Armor,  compound 3J7 

Armor,  effect  of  projectiles  on 320 

Armor,  improved  fastenings  for 323 

Armor,  kinds  of .*....  317 

Armor,  old,  fastenings  for. 322 

Armor,  penetration  of 325 

Armor-piercing  shell 281 

Armor-plates,  tests  of 324 

Armor,  steel,  history 318 

Armor,  steel,  improvements  , 319 

Arms,  cutting 528 

Arms,  cutting  and  thrusting 531 

Arms,  hand 528 

Arms,  portable 528 

Arms,  small 531 

Arms,  thrusting 529 

Artillery-carriages,  classification 389 

Artillery-carriages,  the  axle 389 

Artillery  sabre,  light , 529 

Assembling  gun 180 

Assembling,  operations  after 182 

Assembling  tube  and  jacket .  .   181 

Attachment  of  horses 403 

Attachment  of  traces 403 

Auxiliary  ballistic  formulas 367 

Auxiliary  ballistic  tables 371 

Auxiliary  ballistic  tables,  examples 372 

Axle-arms - 3go 

Axle,  artillery-carriages „ 389 


INDEX.  641 

B 

PAGE 

Backing * 406 

Backing  for  armor 321 

Ballistic  coefficient  C 35^ 

Ballistic  formulas,  auxiliary c    367 

Ballistic  formulas,  simplification  of 361 

Ballistic  functions,  calculation  of 362 

Ballistic  problems,  table  of 388 

Ballistic  superiority  of  smokeless  powders,  cause  of 132 

Ballistic  tables,  auxiliary 37I 

Ballistic  tables,  auxiliary,  examples  of  use  of 372 

Ballistic  tables,  explanation  of . , 369 

Ballistic  test  of  projectiles » 317 

Ballistics,  exterior /. 347 

Ballistics,  interior  31 

Ballistics,  practical  problems 374 

Ballistite 127 

Bands,  copper 307 

Bands  or  belts 159 

Barrel,  length  of,  in  small  arms 545 

Barrel,  small-arm 532. 

Barrel,  thickness  of < 544. 

Barbette  carriages  .  .    418 

Base-plate 420 

Bases,  chemically  active,  dynamite 1 16- 

Bases,  high  explosive,  with  dynamite 117- 

Bashf orth  target 97 

Bayonet 530 

Belleville  springs , 398 

Bellite 120 

Belts 159 

Belts  or  bands 159 

Berthelot's  theory 106 

Binomial  formula,  limit  of  use  of 62 

Binomial  formula,  Sarrau's 53 

Blasting,  use  of  dynamite  in 116 

Blasting,  use  of  gun-cotton  in 113 

Blasting,  use  of  n  itro-glycerine  in..., 115 

Blending  and  marking  gunpowder 2 

Blow-holes  in  gun-steel 140 

Bolt,  cal.  .30 555 

Bore,  length  of 45 

Bore  of  tube  180 

Boring  and  turning 152 

Boring-  and  turning-lathes 179 

Boring,  finish 182 

Boring  tube,  first 177, 


642  INDEX. 

PAGE 

Bormann  fuze  332 

Boxer  oblong  shrapnel . 290 

Boxer  spherical  shrapnel 289 

Brake,  Buffington 397 

Brake,  Hotchkiss 395 

Brake,  hydraulic,  with  constant  orifice. . .  - 456 

Brake,  Lemoine 395 

Brake,  necessity  for 453 

Brake,  Nordenfelt 396 

Brake  with  variable  orifice 460 

Brakes  394 

Brakes  and  buffers 453 

Brakes,  classes  of , 454 

Brakes,  conditions  for  good 454 

Brakes,  elastic 397 

Brakes,  friction 394 

Brakes,  friction,  for  seacoast  guns 454 

Brakes,  hydraulic 399~455 

Brakes,  hydraulic,  classification 456 

Breech-block,  field-artillery 237 

Breech-block,  seacoast  guns   260 

Breech-block,  Springfield 553 

Breech-loading  projectile 306 

Breech-loading  projectile,  rotating  device 306 

Breech,  maximum  pressure  on 55 

Breech  mechanism 548 

Breech  mechanism,  action  of,  seacoast  guns 266 

Breech  mechanism,  cal.    30 544 

Breech  mechanism,  classification  , 548 

Breech  mechanism,  Farcot 270 

Breech  mechanism,  field-guns,  action  of 249 

Breech  mechanism,  improved,  continuous  rotation 269 

Breech  mechanism,  improvements  in 269 

Breech  mechanism,  Krupp's   274 

Breech  mechanism  of  field-artillery 236 

Breech  mechanism  of  siege-guns 252 

Breech  mechanism,  requirements 551 

Breech  mechanism,  rotating 549 

Breech  mechanism,  seacoast  guns 259 

Breech  mechanism,  sliding , 548 

Breech  mechanism,  Springfield  rifle 552 

Breech  mechanism,  12-inch  mortar , 268 

Breeching 408 

Breger's  improvements 94 

Brinell's  experiments.. .  .    154 

Broadwell  ring 276 

Brown  powder 7 


INDEX.  643 

PAGE 

Brown  segmental  gun 220 

Bruce  feed 595 

Brugere's  powder 118 

Buffer,  Englehardt 397 

Buffers,   8-inch ' 442 

Buffers  and  brakes 453 

Buffi ngton  brake 397 

Buffington-Crozier  disappearing  carriage 430 

Built-up  guns,  general  principles 205 

Bullet 584 

Bullet,  cal.  .30 585 

Bullet,  Hebler 585 

Bullet,  reduction  of  weight  of 535-537 

Bullet,  Springfield 585 

Burning  of  spherical  grain  under  pressure 50 

Bursting-charge  of  shell 284 

Bursting-charge  of  shrapnel,  position  of 292 

Bursting  of  shell '. 284 

Butler  projectile 305 


c 

Calculations  for  compound  cylinder 206 

Calculation  of  ballistic  functions 262 

Calculation  of  pi 212 

Calculation  of  shrinkage 214 

Calculation  of  value  of  r 65 

Calibre,  advantages  of  reduction  of 538 

Calibre,  effect  of,  smokeless  powder 123 

Calibre,  reduced,  disadvantages  of 540 

Calibre,  .30,  breech  mechanism 554 

Calibre,  .30,  bullet 585 

Calibre,  .30.  firing  mechanism 560 

Calibre,  .30,  magazine]  for 577 

Calibre,  .30,  receiver 547 

Calibre,  .30,  sights  for 565 

Calibres  of  seacoast  guns 254 

Calipers 226 

Calipers,  eccentric 316 

Cam-latch 553 

Canister » 285 

Canister,  Sawyer 286 

Cannon,  classification  of  232 

Cannon,  description  of 232 

Cannon,  Hotchkiss  revolving 614-616 

Cannon  powder 5 

Cannon,  targets  for 84 


644  INDEX. 

PAGE 

Carbo-dynamite TI7 

Carriage,  direction  of 4°6 

Carriage,  8-inch  barbette -   4*8 

Carriage,  Hotchkiss  mountain 409 

Carriage,  howitzer 410 

Carriage,  siege-mortar • 41 7 

Carriage,  3.6-inch  mortar 4!° 

Carriages,  artillery /. 3§9 

Carriages,  barbette 4T§ 

Carriages,  casemate 4°° 

Carriages,  disappearing 428 

Carriages,  field-artillery 409 

Carriages,  field,  3.2-inch  411 

Carriages,  mountain-artillery 409 

Carriages,  old  U.  S.  seacoast 432 

Carriages,  seacoast 418 

Carriages,  siege 41 5 

Carriages,  turret 428 

Carriages,  wheeled,  recoil  of 450 

Carrier-ring  242 

Cartridge-case 586 

Cartridges,  folded  head 582 

Cartridges,  folded  head  cup  anvil 583 

Cartridges,  solid  head : 584 

Case,  cartridge 586 

Case-shot 584 

Case-shot,  definition  of 284 

Case,  spherical  U.  S 288 

Casemate  carriages.. 428 

Cases  in  pointing 467 

Casting  ingots 146 

Casting  projectiles 313 

Casting,  treatment  after 149 

Causes  affecting  resistance  of  air 351 

Causes  of  deviation  in  pointing 476 

Cavalry  sabre 531 

Centre  of  impact 499 

Chamber,  profile  of,  cal.  .30 , 544 

Changes  in  black  powders 121 

Changes  of  velocity,  pressure  constant 70 

Characteristics  a  and  /? 55 

Chassis,  8-inch   .' 420 

Chauvenet's  table 521 

Chemical  action  of  smokeless  powders 131 

Chemical  composition  of  gun-steel  136 

Chemical  formula  for  combustion  of  powder 19 

Chilled  cast-iron  armor 317 


INDEX.  645 


PAGE 


•Chilled  shot 280 

Chromium  in  gun-steel 137 

Chronograph,  Le  Boulenge 85 

Chronoscope,  Schultz 95 

Classes  of  brakes 454 

Classification  of  artillery-carriages 389 

Classification  of  breech  mechanism 548 

Classification  of  cannon 232 

Classification  of  fuzes 328 

Classification  of  projectiles 279 

Classification  of  repeating  mechanism 569 

Classification  of  smokeless  powders 126 

Close  vessel,  combustion  in 19 

Cocoa  powder 7 

Cocoa  powder,  velocity  of  emission  for 16 

Coefficient,  ballistic,  C 354 

Cooling  jacket 182 

Combination  fuzes 337 

Combination  fuze,  Frankford  Arsenal 337 

Combustion  in  a  close  vessel 19 

Combustion  of  gunpowder,  chemical  formula  for 19 

Combustion  of  gunpowder  in  air 9-10 

Combustion  of  gunpowder  in  air,  laws  of 10 

Combustion  of  gunpowder  in  a  gun • 31 

Common  electric  primers . .  • 343 

Common  features  of  field-guns 234 

Common  features  of  seacoast  guns 254 

Common  features  of  siege-guns 251 

Common  friction-primers. ...  , 342 

Comparator,  standard 221 

Comparison  of  mean  and  true  mean  errors 515 

Composition  of  gunpowder I 

Composition  of  products,  Noble  and  Abel's  experiments 23 

Compound  armor 317 

Compound  cylinder,  calculations  for 206 

Compound  cylinder,  longitudinal  strength  of 209 

Compounds,  explosive 105 

Compounds,  nitro-  substitution 106 

Compression,  smokeless  powder 124 

Conditions  for  good  brake 454 

Conditions  for  good  magazine-gun 568 

Conditions  to  be  fulfilled  by  smokeless  powders 129 

Cone  of  dispersion,  cause  affecting  it 287 

Cone  of  dispersion,  shrapnel 286 

Cones,  speed 160 

Connection  by  cords 161 

'Connection,  hydraulic 161 


646  INDEX, 

PAGE. 

Console <  •• 263 

Constant  orifice,  length  of  recoil 45& 

Constituents,  other,  of  gun-steel J36' 

Construction  of  spherical  shrapnel 288 

Contact,  rolling , 15& 

Contact,  sliding J57 

Continuous  rotation,  improved  breech  mechanism 269 

Copper  bands 3°7 

Core  of  projectile  311 

Cored  shot 279 

Cordite 128 

Cords,  connection  by 161 

Correction  for  drift 4°9 

Cover,  vent 247 

Crane  140 

Cranes - 149 

Crozier  gun 220 

Crucible  process 145 

Crusher-gauge,  Noble's  . .    101 

Curve  of  stresses  in  cylinder 193 

Curve  of  total  recoil 449 

Curve,  pressure,  Longridge  78 

Curve,  pressure,  Mayevski 78 

Curve,  pressure,  Noble  and  Abel's 77 

Curve,  pressure,  Sarrau 80 

Curve,  probability 506 

Curved  fire 348 

Curves,  pressure,  in  guns 76 

Cut-off,  magazine,  cal.  .30 548 

Cutting-arms 528 

Cutting-  and  thrusting-arms % 531 

Cutting-tools 164 

Cutting  up  smokeless  powder 125 

Cutters,  milling 165 

Cylinder,  compound,  calculations  for 206 

Cylinder,  curve  of  stresses  in 193 

Cylinder,  maximum  strains  in 198 

Cylinder,  method  of  strengthening , 196 

Cylinder,  pressure  in 465 

Cylinder,  pressure  in,  constant  orifice 459 

Cylinder,  states  of ...  206 


D 

Dangerous  space 381 

De  Bange  obturator 238 

Decrease  in  weight  of  cartridge 530, 


INDEX.  647 

PAGE 

Deduction  of  final  equation  of  motion  of  projectile  in  bore < .  50 

Defects  of  gun-steel 140 

Definition  of  case-shot , , 284 

Definition  of  fuze 328 

Definition  of  gun-steel 136 

Definition  of  machine 155 

Definition  of  shell 281 

Delayed-action  fuzes 340 

A  constant,  o3  and  r  variable .' 71 

Density,  influence  of,  gunpowder 18 

Density  of  dynamite  No.  i 116 

Density  of  explosive  gelatine 117 

Density  of  gun-cotton 112 

Density  of  loading  2 1 

Density  of  loading,  French  measure  for 22 

Density  of  mercury  fulminate 119 

Density  of  nitro-glycerine 114 

Density,  sectional , 296 

Density,  spherical , 310 

Depression  range-finders 481 

Depth  of  grooves 543 

Description  of  cannon 232 

Description  of  gun 176 

Description  of  latch 243 

Description  of  Le  Bouleng6  chronograph 86 

Description  of  modern  shrapnel 292 

Designolle's  powder 1 1 8 

Detachable  magazines 569 

Details  of  modern  rotating  band 308 

Determination  of  a  and  ft. 67 

Detonation  by  influence 108 

Detonation  of  dynamite ...    1 16 

Detonation  of  explosive  gelatine 118 

Detonation  of  gun-cotton 113 

Detonation  of  mercury  fulminate 119 

Detonation  of  nitro-glycerine 115 

Detonating  fuze 108 

Detonators 107 

Deviations 498 

Deviations,  how  measured 498 

Deviations  in  pointing,  causes  of 476 

Devices,  elevating 399 

Devices,  rotating 302 

Diameters,  exterior,  measuring 226 

Diameters,  interior,  measuring 230 

Difficulties  in  making  time-fuzes 328 

Direct  fire ." 348 


648  INDEX. 

PACE 

Direction  of  carriage •  • '• 406 

Direction  of  traces 4°5 

Direction  of  twist £44 

Disadvantages  of  reduced  calibre.    54° 

Disappearing  carriages * 428 

Disappearing  carriage,  Buffington-Crozier 430 

Disappearing  carriage,  Gordon 431 

Discussion  of  formula  for  pressure  of  gunpowder 28 

Dish  of  wheel 391 

Disjunction 89 

Disjunction,  fixed 89 

Disjunction  reading,  fixed,  Le  Boulenge 93 

Disjunctor 91 

Distance-rings,  rollers  and 420 

D istances  by  eye 478 

Distances  by  sound 478 

Distances,  estimating 477 

Distribution  of  energy  in  shops 162 

Division  of  trajectory. 505 

Division  of  work  of  gunpowder 41 

Double  position,  rule  of 382 

Draught 401 

Draught-harness 408 

Draught-horse 402 

Drift 348,  350,  385 

Drift,  correction  for 469 

Drift,  permanent  angle  of 473 

Driggs-Schroeder  rapid-fire  gun 629 

Drill-press 173 

Drill  press,  action  of 174 

Drill-press,  parts  of 173 

Drills  and  reamers 165 

Drying  and  dusting  gunpowder 2 

Drying  smokeless  powder 125 

Dynamic  method 102 

Dynamic  method,  pressure  by,  Noble  and  Abel's 102 

Dynamite : 115,  116 

E 

Eprly  shrapnel 288 

Eccentric  calipers 316 

Eccentricity  of  projectiles 315 

Effect  of  calibre,  smokeless  powder 123 

Effect  of  projectiles  on  armor 320 

Effect  of  variation  of  powder,  Noble  and  Abel's  experiments 24 

8-inch  barbette  carriage 418 


INDEX.  649 


8-inch  chassis 420 

8-inch  converted  rifle ...  273 

8-inch  gun 254 

8-inch  top  carriage  and  buffers 422 

Elastic  brakes 397 

Elastic  strength  of  guns 185 

Elasticity  and  elastic  limit  of  gun-steel 137 

Elasticity,  modulus  of 139 

Electric  primer,  common 343 

Electric  primer,  obturating 346 

Elements  of  loading,  variation  of 69 

Elevating  devices 399 

Elevating  devices,  8-inch 423 

Elevating  gear,  12-inch  mortar  carriage 427 

Elevating-screw 399 

Emmens  acid   118 

Emmensite 119 

Emission,  velocity  of,  spherical  grain 14 

Energy,  distribution  of  in  shops 162 

Energy  of  rotation  of  oblong  projectiles 294 

Energy,  relative,  of  smokeless  powders 129 

Englehardt  buffer 397 

Equation  of  motion  of  projectile  in  bore 47 

Equation  of  pressure  curve,  Noble  and  Abel's  method 33 

Equation  of  pressure  curve,  recent  hypothesis 37 

Equation  of  probability  curve 507 

Equations  A,  integration  of 358,  360 

Error,  law  of 505 

Error,  probable 512 

Error,  true  mean 513 

Errors .' 502 

Errors  and  corrections  in  general  equation  of  motion  of  projectile 49 

Errors  in  height  of  sight  in  pointing 485 

Errors  in  pointing 472 

Estimating  distances 477 

Ether,  nitric 106 

Eureka  projectile '. 305 

Example,  rule  of  double  position 383 

Examples  of  use  of  auxiliary  ballistic  tables. 372 

Expanding  system,  projectiles * 304,  305 

Expansion,  furnace  for,  guns 181 

Expansion,  parts  of  guns 181 

Experiment,  pressure  by,  gunpowder 98 

Experiments,  Brinell's 154 

Experiments  on  resistance  of  air 351 

Explanation  of  ballistic  tables , 369 

Explosion,  modes  ot  producing 108 


650  INDEX. 


Explosion  of  gunpowder » 9 

Explosion,  orders  of . . 106 

Explosion,  temperature  of,  gunpowder 30 

Explosive  compounds 105 

Explosive  gelatine 117,118- 

Explosive.  high 105 

Explosive,  low 105 

Explosive  mixtures 1 05 

Explosive,  strength  of 109 

Explosives 105 

Explosives,  flameless 120 

Explosives,  principal in 

Exterior  ballistics 347 

Exterior  ballistics,  problem  1 375 

Exterior  ballistics,  problem  2 376 

Exterior  ballistics,  problem  3 ,. 377 

Exterior  ballistics,  problem  4 378 

Exterior  ballistics,  problem  5 380 

Exterior  ballistics,  problem  6 381 

Exterior  ballistics,  problem  7 386 

Exterior  diameters,  hoops 226,  231 

Exterior  of  cylinder,  strain  at 203 

Exterior  pressure,  method  of  applying,  guns 205 

Exterior  pressure,  thickness  to  resist,  cylinders 203 

Exterior  pressures,  limiting,  cylinders 201 

Extractor,  cal.  .30 557 

Extractor,  Springfield 554 

Eye,  errors  of  in  pointing 485 

F 

Factor  of  effect,  gunpowder 37 

Farcot  breech  mechanism 270 

Fastenings  for  armor,  improved 323 

Fastenings  for  old  armor 322 

Feed,  Accles,  Galling 507 

Feed,  Bruce,  Galling , gor 

Feed-case,  tin,  Galling ege 

Feed,  latest,  for  Galling ggg 

Feed  of  lathe !68 

Feeds  for  Galling  guns 504 

Field-artillery,  breech-block 237 

Field-artillery,  breech  mechanism 236 

Field-artillery,  principal  parts  of  breech  mechanism 236 

Field-  and  siege-guns,  table  of 253 

Field-carriage,  3.2-inch 4II 

Field-guns 234,  235 


INDEX.  6$I 

PAGE 

Field-guns,  common  features 234 

Field-limber 412 

Field-shell 283 

5-inch  siege-carriage 415, 

5-inch  siege-gun 251 

15-inch  Rodman  smooth  bore 274 

Figures  of  teeth 158 

Final  equation,  integration  of,  interior  ballistics 53 

Final  equation  of  motion  of  projectile  in  bore 52 

Final  equation  of  motion  of  projectile  in  bore,  deduction  of So- 
Final  velocity 348 

Finish-boring 182 

Fire,  curved 34$ 

Fire,  direct 348 

Fire,  high  angle 348 

Fire,  indirect 34$ 

Fire,  mortar 386 

Fire,  probability  of 505 

Firing  mechanism,  cal.  .30 560 

Firing  mechanism,  small  arms 558 

Firing  mechanism,  Springfield , 559. 

Firminy  process 280 

First  boring  of  gun-tube 177 

Fiske  position-finder 483 

Fiske  rangerfinder 482 

Fixed  box  magazine , 575 

Fixed  disjunction 89, 

Fixed  magazines 571 

Fixed  powder-chamber. 72 

Fixing  disjunction  reading,  Le  Bouleng6 93 

Flameless  explosives 120 

Flanged  projectiles 303 

Flask,  moulding 312 

Flat  grain  powder,  velocity  of  emission  for 16 

Flatness  of  trajectory 538 

Flight,  time  of,  projectiles 377 

Fluid-compression,  Whitworth's 147 

Fluid-compression  theory 148 

Folded-head  cartridges 582 

Folded-head  cup-anvil  cartridges 583 

"  Force  "  of  powder 29 

Force  or  pressure no 

Forces  acting  on  projectile 348 

Foreign  guns 274 

Forging,  hydraulic,  Whitworth's 150- 

Forgings,  gun 152,  177 

Forgings,  tests  of  gun 155 


652  INDEX 

PAGE 

Form  of  dynamite  No.  i ' * 

Form  of  explosive  gelatine l 

Form  of  grain  of  gunpowder. 

Form  of  gun-cotton * 

Form  of  head  of  projectile 3™ 

Form  of  mercury  fulminate "9 

Form  of  nitro-glycerine I:4 

Form  of  picric  acid * 

Form  of  projectile 3°9 

Forms  of  pieces  in  rolling  contact J57 

Formula,  binomial,  Sarrau's 53 

Formula  for  burning  in  air  of  grains  of  gunpowder  of  different  shapes n 

Formula  for  pressure  of  gases,  Noble  and  Abel's  experiments 26 

Formula,  monomial,  for  velocity 63 

Formulas,  auxiliary  ballistic 3^7 

Formulas  for  whole  range - 3°5 

Formulas,  penetration 325 

Formulas,  Sarrau's 4° 

Formulas,  useful  practical 75 

Fouling,  smokeless  powders I31 

4.2-inch  Parrott  siege-gun 273 

4  5-inch  siege-gun 272 

Frankford  Arsenal  combination  fuze 331 

Frankford  Arsenal  shrapnel 292 

Free  acids,  effect  on  dynamite. 116 

Free  acids,  effect  on  gun-cotton 113 

Free  acids,  effect  on  nitro-glycerine 114 

French  measure  for  density  of  loading 22 

Frey re  obturator 240 

Friction-brakes 394 

Friction-brakes,  seacoast 454 

Friction-primer,  common 342 

Friction-primer,  obturating 344 

Front  sight 466,  563 

Front  sight,  cal.  .30 566 

Front  sight,  Springfield   565 

Fulminate  of  mercury. . . , 1 19 

Fulminates 119 

Furnace 180 

Furnace  for  expansion , 181 

Furnace,  open-hearth  process 144 

Fusibility  of  gun-steel 141 

Fuze,  Bormann , 328 

Fuze,  definition  of 328 

Fuze,  detonating 108 

Fuze,  Frankford  Arsenal  combination 337 

Fuze,  Hotchkiss  base  percussion 336 


INDEX.  653 

PAGE 

Fuze,  Hotchkiss  front  percussion 334 

Fuze,  mass  of 108 

Fuze,  Merriam  delayed  action 340 

Fuze,  mortar 330 

Fuze,  seacoast 331 

Fuzes  and  primers 328 

Fuzes,  classification 328 

Fuzes,  combination 337 

Fuzes,  delayed  action 340 

Fuzes,  old,  in  use 330 

Fuzes,  percussion .   333 

Fuzes,  time , ,. 328 


G 

Gas-check,  Krupp  mechanism 276 

Gas-producer 142 

Gate  and  riser 313 

Galling  gun „ 590-593 

Galling  gun,  feeds   •. 594 

Galling,  latest  feed < 598 

Gardner  machine-gun 600,  601-603 

Gauge,  step 227 

Gelatine,  explosive 117 

General  arrangement  of  machine-shop 162 

General  features  of  Krupp  mechanism 277 

General  principles  of  built-up  guns 205 

General  principles  of  measurements,  guns 229 

Glazing  gunpowder , 2 

Gordon  disappearing  carriage 431 

Grain,  form  of,  gunpowder •. 5 

Graining  gunpowder 2 

Grape-shot     285 

Gravimetric  density  of  gunpowder 4 

Grooves,  kinds  of 301 

Grooves,  depth  of 543 

Grooves,  number  of 542 

Grooves,  width  of 542 

Gruson  turrets 317 

Guide-rails,  seacoast-guns   264 

Gum-dynamite , 117 

Gunners'  quadrant   , 491 

Gun,  assembled 180 

Gun,  Brown  segmental 220 

Gun-conslruction,  measurements  in 216 

Gun-cotton in,  112,  113 

Gun-cotton,  modification  of , 122 


INDEX. 


Gun,  Crozier 220 

Gun,  description  of,  general 1 76 

Gun,  Driggs-Schroeder  rapid  fire 627,  629 

Gun,  8-inch 254 

Gun-forgings 152,  177 

Gun-forgings,  tests  of 153 

Gun,  Galling 59°.  59r>  592,  593 

Gun,  Gardner 600 

Gun,  Hotchkiss  rapid  fire 620 

Gun,  length  of 218 

Gun-manufacture 1 76 

Gun,  Maxim  rapid  fire 631,  633 

Gun,  Nordenfelt  rapid  fire 624,  625 

Gun,  parts  of.... 176 

Gun  steel 136,  137,  139.  J4o,  141,  142 

Gun,  Woodbridge 219 

Gunpowder,  action  of  in  a  gun ....     31 

Gun  powder,  blending  and  marking „ 2 

Gunpowder,  combustion  in  air .' 9,  10 

Gunpowder,  combustion  of  in  a  gun 31 

Gunpowder,  composition  of i 

Gunpowder,  drying  and  dusting 2 

Gunpowder,  explosion  of 9 

Gunpowder,  form  of  grain 5 

Gunpowder,  "  force  "of 29 

Gunpowder,  formula  for  burning  in  air  of  grains  of  different  shapes n 

Gunpowder,  formula  for  burning  in  air  of  spherical  grains 12 

Gunpowder,  glazing  and  graining 2 

Gunpowder,  gravimetric  density 4 

Gunpowder,  history  of 9 

Gunpowder,  ignition  of 9 

Gunpowder,  incorporating 2 

Gunpowder,  inflammation  of 10 

Gunpowder,  inspection  of 8 

Gunpowder,  irregular  granulation 5 

Gunpowder,  laws  of  combustion  in  air 10 

Gunpowder,  manufacture  of I 

Gunpowder,  mixing  ingredients  of I 

Gunpowder,  pressing   2 

Gunpowder,  proof  of 8 

Gunpowder,  pulverizing  ingredients I 

Gunpowder,  regular  granulation    j 

Gunpowder,  Rodman's  improvement  of 9 

Gunpowder,  specific  gravity 3 

Gunpowder,  work  of  , .  36,  38,  39 

Guns 136 

Guns,  built  up,  general  principles 205 


INDEX.  655 


PAGJ 


Guns,  elastic  strength  of. , 185 

Guns,  field 234 

Guns,  foreign 274 

Guns,  machine 589 

Guns,  machine  and  rapid  fire 589 

Guns,  old,  in  U.  S.  service 272 

Guns,  rapid  fire 619 

Guns,  seacoast 254 

Guns,  siege 251 

Guns,  10-  and  12-inch 256 

Guns,  thickness  of  walls 217 

Guns,  wire 218 


H 

Hammer,  steam 150 

Hand  arms 528 

Handle,  lever 246 

Hardening  of  gun-steel 141 

Hardness  of  gun-steel 137 

Harness,  artillery 406 

Harness,  draught 408 

Harvey-process,  armor 319 

H  eadgear 407 

Head  of  projectile,  form  of 310 

Heat,  amount  of,  Noble  and  Abel's  experiments 24 

Heat  and  cold,  effect  of  on  dynamite 1 16 

Heat  and  cold,  effect  of  on  explosive  gelatine 117 

Heat  and  cold,  effect  of  on  gun-cotton 113 

Heat  and  cold,  effect  of  on  nitro-glycerine 114 

Hebler  bullet 585 

H  eight  of  rear  sight 468 

H  eight  of  trajectory 380 

Height  of  trajectory,  maximum 380 

Hellhoffite 120 

Hexagonal  powder 7 

H  igh-angle  fire 348 

H igh  explosives 105 

H  igh  explosives  and  smokeless  powders,  table  of 133 

High-explosive  bases,  dynamite 117 

Hinge-pin,  Springfield  rifle 533 

History  of  ammunition   581 

History  of  gunpowder g 

History  of  rapid-fire  guns 619 

History  of  smokeless  powder,  early 122 

Holtzer  shot 280 

Hooke's  law,  elasticity 138 


656  INDEX. 

PAGE 

Horses,  attachment  of 4°3 

Horse,  work  of 4O1 

Hotchkiss  brake 395 

Hotchkiss  base-percussion  fuze 33& 

Hotchkiss  breech-loading  projectile 307 

Hotchkiss  front-percussion  fuze 334 

Hotchkiss  mountain-carriage 409 

Hotchkiss  mountain-rifle 232 

Hotchkiss  muzzle-loading  projectile 304 

Hotchkiss  rapid-fire  gun 620,  622 

Hotchkiss  revolving  cannon 614,  616 

Hotchkiss  shrapnel 293 

Howitzer  carriage 416 

Howitzer,  7-inch 252 

Hydraulic  brakes 399,  455 

Hydraulic  brake  with  constant  orifice 456 

Hydraulic  buffer,  1 2-inch  mortar  carriage 425 

Hydraulic  connection 161 

Hydraulic  forging,  Whitworth 150 

I 

Ignition  of  explosive  gelatine , 117 

Ignition  of  gun-cotton 113 

Ignition  of  gunpowder 9 

Ignition  of  nitro-glycerine 114 

I.  K.  powder 6 

Impact,  centre  of 499 

Improved  breech  mechanism,  continuous  rotation 269 

Improved  fastenings  for  armor 323 

Improvements,  Breger's,  ballistic  instrument 94 

Improvements  in  breech  mechanism t .  269 

Inclination,  angle  of,  exterior  ballistics 378 

Incorporating  gunpowder 2 

Increase  of  accuracy,  small  arms 539 

Increased  penetration,  small  arms 540 

Increasing  twist 300 

Indirect  fire 348 

Indirect  pointing 475 

Inert  absorbents,  dynamite 115 

Infinite  expansion,  gunpowder 37,  41 

Inflammation  of  gunpowder 10 

Influence,  detonation  by .   108 

Influence  of  passive  resistance  on  velocity  and  pressure 46 

Ingot-molds I46 

Ingots,  casting I46 

Initial  air-space,  reduced  length  of 40 


INDEX.  657 


Initial  velocity ,  . . .  348 

Initial  velocity  by  experiment 83 

Inspection  and  proof  of  projectiles 314 

Inspection  of  gunpowder 8 

Integration  of  equation  A 358,  360 

Integration  of  final  equation  of  motion  of  projectile  in  bore 53 

Interior  ballistics 31 

Interior  diameters 230 

Interior  diameters  of  long  hoops 230 

Interior  diameters  of  long  tubes 224 

Interior  diameters  of  short  hoops,  measurements  of 222 

Interior  pressures,  limiting 200 

Interior  pressure   thickness  to  resist,  cylinder 201 

Irregular  granulation,  gunpowder 5 

Iron,  kind  of  for  projectiles 313 

J 

Jacket,  cooling 182 

Jarmann  magazine-rifle 571 

Jump 348,  488 

K 

A',  value  of  interior  ballistics 57 

KQ,  value  of  interior  ballistics 57 

Kieselgiihr , 115 

Kind  of  iron,  projectiles 313 

Kinds  of  armor . 317 

Kinds  of  grooves 301 

Krupp  mechanism 274 

Krupp  mechanism,  advantages  and  disadvantages * / 277 

Krupp  mechanism,  gas-check : 276 

Krupp  mechanism,  general  features 277 

Krupp  mechanism,  locking-screw 275 

L 

Ladle,  casting 146 

Lame's  first  law 190 

Lame's  second  law 191 

Lance  or  pike 531 

Latch,  description  of,  breech  mechanism 243 

Latch,  object  of  field-artillery 243 

Latch,  side,  seacoast-artillery 265 

Latch,  tray,  seacoast-artillery 265 

Latest  steel  plates    , 319 

Lathe..                                   ,.  166 


INDEX. 

PACK 

Lathe,  action  of 169 

Lathe,  boring  and  turning 179 

Lathe,  feed 168 

Lathe,  parts 167 

Lathe,  slide-rest 168 

Law,  Hooke's 138 

Law,  Lame's  first 190 

Law,  Lame's  second 191 

Law  of  error 505 

Law  of  variation  of  orifice,  buffer 463 

Lazy-tongs 401 

Lee  magazine 570 

Le  Boulenge  chronograph 85-88,  93,  94 

Le  Boulenge  telemeter 478 

Lemoine  brake 395 

Length  of  barrel,  small  arms 545 

Length  of  bore,  guns 45 

Length  of  gun 218 

Length  of  recoil 448 

Length  of  recoil,  constant  orifice 458 

Length  of  recoil,  variable  orifice. .  .-. 461 

Lengths,  measurements  of 227 

Leonard  powder 128 

Letard's  apparatus 103 

Lever-handle 246 

Levers,  elevating 401 

Light  artillery  sabre 529 

Light,  effect  of  in  pointing 485 

Limber,  field 412 

Limit  of  use  of  binomial  formula , 62 

Limiting  exterior  pressures , 201 

Limiting  exterior  pressure  on  tube 211 

Limiting  interior  pressures , 200 

Limits  of  the  modulus 75 

Line  of  fire 347 

Line  of  sight 347 

Linkwork 160 

Loading,  density  of 21 

Loading-scoop,  12-inch  mortar  carriage 428 

Locking-screw,  Krupp  mechanism , 275 

Longitudinal  strength,  single  cylinder 203 

Longitudinal  strength,  compound  cylinder . .  „ 209 

Longitudinal  stress  and  strain 187 

Longridge's  pressure  curve 78 

Low  explosive 105 


JiylS* 

*A          OJf 

INDEX.  659 

M 

PAGE 

M,  value  of 55 

Machine  and  rapid-fire  guns 589 

Machine,  definition  of 155 

Machine-guns   589 

Machine-gun,  Gardner 601,  603 

Machine-gun,  Maxim  automatic 605,  606,  608,  610,  612 

Machine,  milling 174 

Machine,  rifling 182 

Machine-shops,  general  arrangement  of 162 

Machine-tools 163 

Machines  in  general  use 166 

Machines  used  in  gun-manufacture 155 

Magazine  cut-off,  cal.  .30 • 548 

Magazine,  fixed  box 575 

Magazine  for  cal.  .30 577 

Magazine-gun,  conditions  for  good 568 

Magazine,  Jarmann   571 

Magazine,  Lee 570 

Magazine,  Mannlicher 575 

Magazine  or  repeating  arms 567 

Magazine,  tubular 571,  574 

Magazines,  detachable 569 

Magazines,  fixed 571 

Malleability  and  ductility  of  gun-steel 141 

Mammoth  powder 6 

Mannlicher  magazine 575 

Mandrils,  forging 151 

Manganese  in  gun-steel 137 

Manufacture,  gun 176 

Manufacture  of  gunpowder I 

Manufacture  of  gun-steel 142 

Manufacture  of  projectiles 311 

Manufacture  of  smokeless  powder,  operations  in 123 

Manufacture  of  smokeless  powder,  solution 124 

Manufacture,  safety  and  cost  of,  smokeless  powders 131 

Marcel-Deprez  registers 96 

Martini-Henry  rifle 550 

Mass  of  fuze 108 

Maxim  automatic  machine-gun 605,  606,  608,  610,  612 

Maxim  rapid-fire  gun 631,  633 

Maximum  height  of  trajectory 380 

Mazimum  pressure  on  base  of  projectile 54 

Maximum  pressure  on  breech 55 

Maximum  strains  on  cylinder 198 

Mayevski's  method,  resistance  of  air 354 

Mayevski,  pressure  curve < 78 


66O  INDEX. 

PAGE 

Mean  error,  true 513 

Mean  radius  of  grain  of  powder 6 

Measuring-points 223 

Measuring-rule 92 

Measurement  of  length 227 

Measurement  of  surface  lengths 228 

Measurements 221 

Measurements,  general  principles  of , 229 

Measurements  in  gun-construction 216 

Measurements,  necessity  for 221 

Measurements  of  interior  diameters  of  long  tubes 224 

Measurements  of  interior  diameters  of  short  hoops 222 

Mechanism,  breech 548 

Mechanism,  breech,  classification 548 

Mechanism,  firing 558 

Mechanism,  rotating 549 

Mechanism,  sliding 548 

Melinite « 119 

Mercury  fulminate 119,  120 

Merriam  delayed-action  fuze 340 

Metal,  quality  of,  for  projectiles 314 

Method  of  applying  exterior  pressure 205 

Method  of  determining  resistance  of  air , 353 

Method  of  strengthening  cylinder 196 

Military  purposes,  use  of  dynamite  for 116 

Military  purposes,  use  of  explosive  gelatine  for 118 

Military  purposes,  use  of  gun-cotton  for 113 

Military  purposes,  use  of  nitro-glycerine  for 115 

Milling-cutters 165 

Milling-machine 1 74,  175 

Mixing  ingredients  of  gunpowder I 

Mixtures,  explosive 105 

Modern  rotating  device  for  projectiles 308 

Modern  shrapnel 291 

Modern  shrapnel,  description  of. 292 

Modes  of  producing  explosion , 108 

Modification  of  gun-cotton 122 

Modulus,  limits  of . . 75 

Modulus  of  elasticity 139 

Modulus  of  precision 510 

Modulus  of  quickness 60 

Modulus,  pressure  as  function  of 62 

Modulus,  velocity  as  function  of 6r 

Molded  powder 7 

Molding  projectiles 312 

Molds,  ingot 146 

Monomial  formula  for  velocity 63 


INDEX.  66 1 

PAGE 

Mortar-carriage,  3.6-inch 410 

Mortar-carriage,  12-inch 423 

Mortar  fire 386 

Mortar  fuze 330 

Mortar  powder 5 

Mortar,  7-inch 252 

Mortar,  3.6-inch 235 

Mortar,  1 2-inch,  breech  mechanism  of 268 

Mortar,  1 2-inch  cast-iron,  steel  hooped 259 

Mortar,  12-inch  steel , , 258 

Motion  of  projectile,  circumstances  of 349 

Motion  of  projectile  in  bore,  equation  of . 47 

Motion  of  projectile  in   bore,  final  equation,  deduction 50 

Motion  of  projectile  in  bore,  final  equation  of 52 

Motion,  transmitted  and  modified,  how 155 

Mountain-carriage,   Hotchkiss 409 

Mountain-guns 232 

Mountings,  small  arms 567 

Muzzle  velocity  by  experiment 83 

N 

Nave 391 

Necessity  for  brake 453 

Necessity  for  measurements » 221 

Necessity  for  rotation  of  oblong  projectile 293 

Nickel  in   gun-steel 137 

Nitre,  addition  of,  to  gun-cotton 112 

Nitric  ethers 106 

Nitro-benzines 120 

Nitro-glycerine 114,  115 

Nitro-  substitution  compounds . . . '. , 106 

Noble  and  Abel's  experiments 19,  20,  22,  23,  24,  25,  26 

Noble  and  Abel's  method  of  determining  pressure  curve 33,  77 

Noble  and  Abel,  pressure  by  dynamic  method 102 

Noble  crusher-gauge 101 

Noble  gauge,  advantages  of 102 

Nomenclature,  compound  cylinder 206 

Nordenfelt  brake 396 

Nordenfelt  rapid-fire  gun 624,  625 

Number  of  grooves 542 

O 

Object  of  latch,  field-artillery 243 

Object  of  Noble  and  Abel's  experiments 22 

Object  of  rapid-fire  guns « 619 


662  INDEX. 

PAGE 

Object  of  wheel • 392 

Oblong  shrapnel 290 

Oblong  shrapnel,  Boxer 290 

Obturating  electric  primer 346 

Obturating  friction-primer 344 

Obturator,  De  Bange 238 

Obturator,  Freyre 240 

Obturator,  seacoast-guns 260 

Oil-tempering  steel , 153 

Old  armor,  fastenings  for 322 

Old  fuzes  in  use 330 

Old  guns  in  U.  S.  service 272 

Old  U.  S.  seacoast-carriages 432 

cS  constant,  A  and  r  variable « 70 

Open-hearth  process 142,  143,  144,  145 

Operation,  open-hearth  process , 145 

Operations  after  assembling,  gun-manufacture 182 

Operations  before  assembling  gun 177 

Operations  in  manufacture  of  smokeless  powder 123 

Orders  of  explosion 106 

Orifice,  area  of,  constant  orifice,  brakes 459 

Orifice,  area  of,  variable  orifice,  brakes 463 

Orifice,  law  of  variation  of,  brakes 463 

Orifice  variable,  brake  with 460 


P 

pi,  calculation  of 212 

/•n,  true  value  of 213 

Pack-horse 401 

Palliser  shot 280 

Paraffine,  effect  of  on  gun-cotton 112 

Parallelopipedon,  velocity  of  emission  for 15 

Parrott  4.2-inch  siege-gun ,  273 

Parrott  projectile i 305 

Parts  of  drill-press 173 

Parts  of  gun. ..  o r  176 

Parts  of  lathe 167 

Parts  of  milling-machine 174 

Parts  of  planer 170 

Parts  of  shaper 171 

Passive  resistances 44 

Passive  resistances,  influence  of  on  velocity  and  pressure 46 

Pattern  of  projectiles 311 

Penetration  formulas 325 

Penetration,  increased,  small  arms 540 

Penetration  of  armor 325 


INDEX.  663 


Percentage  rectangle ,   5!7 

Percussion  fuzes 333,  334 

Periods  of  recoil 435 

Permanent  angle  of  drift 473 

Permanent  gases,  volume  of,  Noble  and  Abel's  experiments 25 

Peyton  powder 128 

Phosphorus  in  gun-steel , 137 

Picrates 118 

Picric  acid 118 

Picric  acid,  powder 126 

Pierted  cylinder,  velocity  of  emission  for,  gunpowder 16 

Pike 531 

Pipes  in  gun-steel 140 

Pitch  of  rifling 542 

Placing  rotating  bands  in  position , 309 

Plane  figure,  probability  of  hitting 522 

Plane  of  fire 347 

Plane  of  sight 347 

Planer , 169,  170,  171 

Pointing 466 

Pointing,  cases  in 467 

Pointing,  errors  in  472,  476,  485,  486,  487 

Pointing,  first  case 468 

Pointing,  fourth  case 473 

Pointing,  indirect 475 

Pointing,  second  case 470 

Pointing,  third  case 470 

Pole,  field-carriage 412 

Pole,  support  of 404 

Portable  arms 528 

Position,  rule  of  double 382 

Position  of  bursting-charge,  shrapnel 292 

Position  of  projectile  in  mold 314 

Position  of  rear  band 309 

Potassium  picrate 118 

Potential no 

Pouring  steel 147 

Powder,  B.  N.  F 127 

Powder-chamber,  fixed 72 

Powder,  picric  acid 126 

Powders,  ammonium  nitrate 126 

Powders,  black,  changes  in 121 

Powders,  progressive 18 

Practical  formulas,  useful 75 

Practical  problems,  ballistics 374 

Precision,  modulus  of 510 

Press,  Whitworth's  hydrauJic 150 


664  INDEX. 

PAGE 

Pressing  gunpowder 2 

Pressure  as  function  of  modulus. 62 

Pressure  by  dynamic  method,  Noble  and  Abel 102 

Pressure  by  experiment 98 

Pressure  curve,  equation  of,  Noble  and  Abel's  method 33 

Pressure  curve,  equation  of,  recent  hypothesis 37 

Pressure  curve  in  guns 76 

Pressure  curve,  Longridge 78 

Pressure  curve,  May evski 78 

Pressure  curve,  Noble  and  Abel 77 

Pressure  curve,  Noble  and  Abel's,  application  of 35 

Pressure  curve,  Sarrau 80 

Pressure,  exterior,  method  of  applying  in  cylinders 205 

Pressure-gauge,  Rodman 100 

Pressure  in  cylinder,  buffer 465 

Pressure  in  cylinder,  constant  orifice. .  , 459 

Pressure,  maximum,  on  base  of  projectile 54 

Pressure  of  gases,  formula  for,  Noble  and  Abel's  experiments 26 

Pressure  of  gunpowder,  discussion  of  formula  for 28 

Pressure  on  breech,  maximum 55 

Pressure  or  force,  explosives ,% no 

Pressures,  limiting,  exterior 201 

Pressures,  limiting,  interior 200 

Primer 587 

Primer,  common  electric 343 

Primer,  common  friction 342 

Primer,  obturating  electric .  346 

Primer,  obturating  friction 344 

Primers 342 

Primers  and  fuzes 328 

Principal  explosives in 

Principal  parts,  breech  mechanism,  field-artillery 236 

Principles  of  teeth  of  wheels 158 

Prismatic  powder 7 

Probable  error 512 

Probable  rectangle 516 

Probable  rectangle  from  mean  error 520 

Probable  zone 514 

Probability  by  right-line  method M 526 

Probability  curve 506,  507 

Probability  of  fire 505 

Probability  of  hitting  plane  figure 522 

Problem  i ,  exterior  ballistics 374 

Problem  2,  exterior  ballistics 376 

Problem  3,  exterior  ballistics 377 

Problem  4,  exterior  ballistics 378 

Problem  5,  exterior  ballistics 380 


INDEX.  665 

PAGE 

Problem  6,  exterior  ballistics 381 

Problem  7,  exterior  ballistics 386 

Problems,  practical,  ballistics 374 

Process,  crucible 145 

Process,  Harvey 3^ 

Process,  open  hearth 142 

Process,  Tresidder 319 

Process,  Whitworth's,  fluid  compression 147 

Producer,  gas 142 

Products,  character  of,  smokeless  powders 131 

Products,  composition  of,  Noble  and  Abel's  experiments 23 

Products,  nature  of,  Noble  and  Abel's  experiments 22 

Profile  of  chamber,  cal.  .30 544 

Profile  of  rib,  constant  pressure. 465 

Progressive  powders 18 

Projectile,  Butler 305 

Projectile,  circumstances  of  motion  of 349 

Projectile,  Eureka 305 

Projectile,  forces  acting  on 348 

Projectile,  Hotchkiss  breech-loading 307 

Projectile,  Hotchkiss  muzzle-loading. 304 

Projectile,  motion  of  in  bore,  equation  of 47 

Projectile,  necessity  for  rotation  of  oblong 293 

Projectile,  oblong,  energy  of  rotation  of 294 

Projectile,  Parrott 305 

Projectile,  position  of  in  mold 314 

Projectile,  rotation  of,  general  discussion 294 

Projectile,  velocity  of 43 

Projectile,  weight  of 310 

Projectile,  Whitworth 303 

Projectiles 279 

Projectiles,  ballistic  test 3r7 

Projectiles,  breech-loading 306 

Projectiles,  casting 313 

Projectiles,  classification  of , » 279 

Projectiles,  core 311 

Projectiles,  eccentricity 3*5 

Projectiles,  effect  of,  on  armor 320 

Projectiles,  flanged. 3°3 

Projectiles,  form  of 309 

Projectiles,  inspection  and  proof  of 3T4 

Projectiles,  kind  of  iron  for 3T3 

Projectiles,  manufacture  of  31  r 

Projectiles,  pattern 3" 

Projectiles,  quality  of  metal  3r4 

Projectiles,  shape  and  dimensions  of 3*5 

Projectiles,  steel. 3*4 


666  INDEX. 


Projectiles,  studded 302 

Proof  of  gunpowder , 8 

Properties  of  probability  curve 507 

Pulley,  rounded 160 

Pulverizing  ingredients  of  gunpowder. .  * I 

Q 

y,  value  of,  interior  ballistics 50 

Quadrant,  gunners' 491 

Quality  of  metal  of  projectiles 314 

Quickness,  modulus  of 60 

R 

» 

Rack-a-rock 120 

Radial  stress  and  strain 185 

Range 348 

Range  by  trial  shots 484 

Range  and  position  finders 482 

Range-finders. . .    479 

Range-finders,  class  1 480 

Range-finders,  classes  2  and  3 481 

Range-finders,  depression  481 

Range-finders,  principle 479 

Range,  whole,  formulas  for. . . 365 

Rapid-fire  gun,  Driggs-Schroeder 627,  629 

Rapid-fire  gun,  Hotchkiss. . . , 620,  622 

Rapid-fire  gun,  Maxim 631,  633 

Rapid-fire  gun,  Nordenfelt 624,  625 

Rapid-fire  guns 619 

Rapid-fire  guns,  ammunition  for 635 

Rapid-fire  guns,  history  of ,  619 

Rapid-fire  guns,  object  of 619 

Rapidity  of  reaction,  explosives no 

Reaction  on  explosion  of  dynamite 116 

Reaction  on  explosion  of  gun-cotton 113 

Reaction  on  explosion  of  mercury  fulminate 119 

Reaction  on  explosion  of  nitro-glycerine 115 

Reaction,  rapidity  of no 

Reamers  and  drills 165 

Reannealing 153 

Rear  band,  position  of 309 

Rear  sight 466,  562 

Rear  sight,  cal.  .30 565 

Rear  sight,  height  of 468 

Receiver,  cal.  .30 547 


INDEX.  667 

PAGE 

Receiver,  small  arms 545 

Receiver,  Springfield  rifle 546 

Recoil,  angle  of  elevation 451 

Recoil,  curve  of  total 449 

Recoil,  discussion  of 437,  438,  440 

Recoil,  example 442 

Recoil,  length  of 448 

Recoil,  length  of,  constant  orifice 458 

Recoil,  length  of,  variable  orifice 461 

Recoil  of  wheeled  carriages 450 

Recoil,  ordinary  case 436 

Recoil,  periods  of 435 

Recoil,  problems 446 

Recoil,  small  arms 532 

Recoil,  steps  in  solution  of  problem 436 

Recoil,  theory  of 434 

Recoil,  time  of,  second  period 447 

Recoil,  velocity  of 43 

Rectangle,  probable 516 

Rectangle,  25  per  cent 516 

Rectangles  of  any  percentage 517 

Reduced  calibre,  disadvantages 540 

Reduced  length  of  initial  air-space 40 

Reduction  of  calibre,  advantages  of 538 

Reduction  of  weight  of  bullet 535,  ^37 

Regenerators 143 

Registers,  Marcel-Deprez 96 

Regular  granulation,  gunpowder -7 

Regulating  magnets,  Le  Bouleng6 93 

Reheating 149 

Reinforce,  axle 390 

Relation  between  x  and  y,  exterior  ballistics 364 

Relations  between  stresses  and  strains,  gun-cylinder 188 

Relative  variation  of  velocity  and  maximum  pressure 74 

Relative  variation  of  velocity  and  time  of  combustion 73 

Remaining  velocity 348 

Remington  rifle 551 

Repeating  mechanisms,  classification  of 560 

Repeating  or  magazine  arms 567 

Requirements  of  breech  mechanism 551 

Rest,  system  at,  gun-construction 210 

Resistance  of  air,  causes  affecting 351 

Resistance  of  air,  experiments  on 351 

Resistance  of  air,  Maye vski's  method 354 

Resistance  of  air,  method  of  determining 353 

Resistance  of  compound  cylinder  in  action 207 

Resistances,  passive,  gunpowder 44 


668  INDEX. 

PACK 

Revolvers 580 

Rib,  profile  of,  constant  pressure,  buffers 465 

Rifle,  8-inch  converted 273 

Rifle,  Hotchkiss  mountain 232 

Rifle,  Springfield,  receiver 546 

Rifle,  3-inch  wrought  iron 272 

Rifling 182,  299 

Rifling-machine 182 

Rifling-tool 183   \ 

Rifling,  uniform 299 

Right-line  method 524 

Right-line  method,  probability  by 526 

Rigidity  of  trajectory ' 384 

Rim  of  wheel * 392 

Ring,  Broad  well 276 

Ring,  carrier 242 

Riser  and  gate 313 

Roburite 120 

Rodman's  improvements  of  gunpowder 9 

Rodman  pressure-gauge 100 

Roller-paths,  12-inch  mortar  carriage 427 

Rollers  and  distance-rings 420 

Rolling  contact 156 

Rolling  contact,  forms  of  pieces 157 

Rolling  smokeless  powder, 125 

Rolling-table 316 

Rotating  band,  modern,  details  of 308 

Rotating  bands,  placing  in  position  of 309 

Rotating  devices 302 

Rotating  devices,  breech-loading  projectiles 306 

Rotating  device,  modern 308 

Rotating  device,  seacoast-guns 262 

Rotating  mechanism,  small  arms 549 

Rotation  of  oblong  projectile,  energy  of 294 

Rotation  of  oblong  projectile ,  necessity  for 293 

Rotation  of  projectile,  general  discussion .» 294 

Rounded  pulley 160 

Rule  of  double  position 382 

Rule  of  double  position,  example 383 

Rule,  measuring 92 


S 

Sabre,  cavalry 531 

Sabre,  light  artillery 529 

Saddle 407 

Safety  mixtures,  Sprengel's 120 


INDEX.  669 

PAGE 

Sarrau's  binomial  formula 53 

Sarrau's  formulas 46 

Sarrau's  pressure  curve go 

Sawyer  canister 286 

Scale  of  time,  Le  Boulenge 85 

Scale  of  time,  Schultz 95 

Scale,  vernier. 231 

Schultz  chronoscope gg 

Scraping-tools 164 

Screw,  elevating 39g 

Seacoast-carriages 4!8 

Seacoast-fuze .  . .-. 331 

Seacoast-guns 254 

Seacoast-guns,  action  of  breech  mechanism 266 

Seacoast-guns,  anti-friction  washers  and  springs 261 

Seacoast-guns,  breech-block 260 

Seacoast-guns,  calibres  and  common  features 254 

Seacoast-guns,  guide-rails 264 

Seacoast-guns,  obturator , 260 

Seacoast-guns,  rotating  devices 262 

Seacoast-guns,  table  of 271 

Seacoast-guns,  translating-screw 264 

Seacoast-guns,  tray 263 

Seacoast-guns,  vent-cover 266 

Seacoast  service,  shells  for 281 

Sebert's  velocimeter 103 

Second  boring  of  tube 178 

Sectional  density 296 

Sector,  toothed 400 

Sensitiveness  of  smokeless  powders 131 

Setting  star  gauge 225 

7-inch  howitzer 252 

7-inch  howitzer  carriage 416 

7-inch  mortar 252 

Shape  and  dimensions  of  projectiles 315 

Shapero . . . . . 171,  172 

Shearing°tools 164 

Shell ........ t 28 1 

Shell  against  decks  of  vessels 282 

Shell,  armor-piercing 281 

Shell,  bursting-charge  of 284 

Shell,  definition  of ". 281 

Shell,  field 2?3 

Shell  for  seacoast  service 281 

Shell,  siege 283 

Shoe 394 

Shot,  case 284 


6/0  INDEX. 

PAGE 

Shot,  chilled 280 

Shot,  cored 279 

Shot,  Holtzer 280 

Shot,  Palliser 280 

Shot,  solid 279 

Shot,  steel .'..   280 

Shrapnel 286 

Shrapnel,  Boxer  oblong 290 

Shrapnel,  Boxer  spherical 289 

Shrapnel,  cone  of  dispersion 286 

Shrapnel,  early 288 

Shrapnel,  Frankford  Arsenal 292 

Shrapnel,  Hotchkiss 293 

Shrapnel,  modern 291 

Shrapnel,  modern,  description  of 292 

Shrapnel,  oblong 290 

Shrapnel,  position  of  bursting-charge 292 

Shrapnel,  spherical,  combustion  of 288 

Shrapnel,  steel  welded 292 

Shrinkage,  calculation  of 214 

Side-latch 265 

Siege-carriage,  5-inch 41 5 

Siege-carriages 4Ig 

Siege-gun,  5-inch 251 

Siege-gun,  4. 5-inch 272 

Siege-gun,  Parrott,  4.2-inch , 273 

Siege-guns 251 

Siege-guns,  breech  mechanism 252 

Siege-guns,  common  features 251 

Siege-mortar  carriage 41y 

Siege-shell 283 

Sight  for  3.2-inch  field-gun 496 

Sight  for  3.6-inch  mortar 495 

Sight,  front 466,  563 

Sight,  rear 466 

Sight,  rear,  height  of -. 453 

Sights 466?  562 

Sights  for  cal.  .30 565 

Sights  for  field-artillery 495 

Sights  for  8-,  10-,  and  12-inch  guns 489 

Sights  for  7-inch  howitzer 493 

Sights  for  siege-artillery 493 

Sights,  rear 562 

Sights,  Springfield  rifle 563 

Silicon  in  gun-steel I37 

Simplification  of  ballistic  formulas 36i 

Sinking-head I47 


INDEX.  671 

PAGE 

Size  of  grain,  density,  progressive  powders 17 

Size  of  grain,  influence  of * I7 

Sleeve,  cal.  .30 556 

Slide-rest,  lathe Z68 

Sliding  contact I57 

SHding  mechanism 548 

Slow  cooling  of  gun-steel 140 

Small-arms  targets 85 

Small  arms » 53! 

Small-arms  powder 5 

Smooth  bore,  15-inch  Rodman 274 

Smokeless  powder,  cutting  up 125 

Smokeless  powder,  drying 125 

Smokeless  powder,  early  history  of 122 

Smokeless  powder,  manufacture,  operation  in 123 

Smokeless  powder,  manufacture  of,  solution 124 

Smokeless  powder,  rolling 125 

Smokeless  powders 121 

Smokeless  powders,  cause  of  ballistic  superiority  of 132 

Smokeless  powders,  classes  i,  2,  and  3 126 

Smokeless  powders,  character  of  products 131 

Smokeless  powders,  chemical  action  of 131 

Smokeless  powders,  classification 126 

Smokeless  powders,  compression 124 

Smokeless  powders,  conditions  to  be  fulfilled  by 129 

Smokeless  powders,  fouling 131 

Smokeless  powders,  relative  energies 129 

Smokeless  powders,  safety  and  cost  of  manufacture 131 

Smokeless  powders,  stability 130 

Smokeless  powders,  sensitiveness 131 

Smokeless  powders,  smokelessness 130 

Smokeless  powders,  velocities  and  pressures 130 

Smokeless  powders,  weight  and  specific  gravity 131 

Solid-head  cartridges 584 

Solid  shot 279 

Solution,  manufacture  of  smokeless  powder r^. .   124 

Solubility  of  explosive  gelatine 117 

Solubility  of  gun-cotton 112 

Solubility  of  mercury  fulminate 119 

Solubility  of  nitro-glycerine 114 

Sound,  distances  by 478 

Space,  dangerous 381 

Speed-cones 160 

Specific  gravity  of  gunpowder 3 

Specific  volume 26 

Spherical  case 288 

Spherical  density 310 


672  INDEX. 


Spherical  grain,  burning  under  pressure 50* 

Spherical  grain,  velocity  of  emission  of 14 

Spherical  grains,  formula  for  burning  in  air ia 

Spherical  shrapnel,  Boxer. . , 289 

Spherical  shrapnel,  construction  of 288 

Sphero-hexagonal  powders 7 

Spokes 391 

Sprengel  safety  mixtures 120 

Springfield  breech-block 553 

Springfield  bullet 585 

Springfield  rifle,  breech  mechanism 552 

Springfield  rifle,  firing  mechanism 559 

Springfield  rifle,  front  sight 565 

Springfield  rifle,  receiver 546 

Springfield  rifle,  sights 563 

Springs,  Belleville , 398 

Springs,  12-inch  mortar  carriage 424 

Stability  of  smokeless  powders 130 

Standard  comparator 221 

Star  gauge 224 

Star  gauge,  setting 225 

Starting  and  stopping  machines 160 

Static  method,  pressure 98 

States  of  cylinder,  gun-construction 206 

Steel  armor 318,  319 

Steel  projectile 314 

Steel  shot 280 

Steel-welded  shrapnel 292 

Step  gauge 227 

Stock , 293,  566 

Stock  and  mountings 566 

Stopping  and  starting  machines 160 

Storage  of  dynamite 116 

Storage  of  explosive  gelatine 118 

Storage  of  gun-cotton  % 113 

Storage  of  mercury  fulminate 120 

Storage  of  nitro-glycerine 115 

Straight  sword 530 

Strain  at  exterior  of  cylinder,  gun-construction 203 

Strains  in  terms  of  radii  and  pressures 197 

Strains,  maximum,  in  cylinder 198 

Strap,  gun-carriage 399 

Strength,  longitudinal,  cylinder 203 

Strength,  longitudinal,  compound  cylinder 209 

Strength  of  an  explosion 109 

Stress  and  strain 185 

Stress  and  strain,  longitudinal. iS; 


INDEX.  673 

PAGE 

Stress  and  strain,  radial 185 

Stress  and  strain,  tangential 186 

Stresses  and  strains,  relation  between 188 

Stresses  in  cylinder,  curve  of 193 

Structure  of  gun-steel I39 

Studded  projectile 302 

Sulphur  in  gun-steel 137 

Summit  of  trajectory 404 

Support  of  pole 404 

Surface  lengths,  measurements  of 228 

Sword,  straight 530 

System  at  rest,  gun-construction 210 

System,  expanding,  projectiles 304,  305 

T 

T,  calculation  of  value  of 65 

r  constant,  GO  and  A  variable 72 

r,  value  of  for  maximum  velocity 59 

Table  I,  probability 511,  512 

Table  II,  use  of,  probabilities 520 

Table  of  ballistic  problems 388 

Table  of  field-  and  siege-guns 253 

Table  of  guns  and  powders 68 

Table  of  high  explosives  and  smokeless  powders 133 

Table  of  seacoast-guns 271 

Tables,  auxiliary  ballistic 371 

Tables,  ballistic,  explanation  of 369 

Tangential  stress  and  strain 186 

Tarage 98 

Target,  motion  of  in  pointing 486 

Targets,   Bashforth 97 

Targets  for  cannon 84 

Targets,  small  arms • 85 

Teeth,  action  of 158 

Teeth,  figures  of 158 

Teeth,  principles  of , 158 

Telemeter,  Le  Boulenge 478 

Temperature  of  explosion  of  gunpowder 30 

10-  and  12-inch  guns » 256 

Tensile  strength  of  gun-steel 137 

Test  for  purity  of  nitro-glycerine 116 

Testing  ingots 149 

Tests  of  armor-plates 324 

Tests  of  gun-f orgings 153 

Theoretical  maximum  velocity 58 

Theory,  Berthelot's 106 


674  INDEX. 

PAGE 

Theory  of  fluid  compression * 148 

Theory  of  recoil 434 

Thickness  of  barrel,  cal.  .30 544 

Thickness  of  walls  of  guns 217 

Thickness  to  resist  exterior  pressure 203 

Thickness  to  resist  interior  pressure 201 

Thickness  to  resist  longitudinal  stress 204 

3-inch  wrought-iron  rifle 272 

3.2-  and  3.6-inch  field-guns , 235 

3. 6-inch  mortar 235 

Thrusting-arms 529 

Time-fuzes 328 

Time-fuzes,  difficulties,  how  overcome 329 

Time-fuzes,  difficulties  in  making 328 

Time  of  burning  for  maximum  velocity,  gunpowder 58 

Time  of  flight 377 

Time  of  recoil,  second  period 447 

Time,  scale  of,  Le  Boulenge 85 

Time,  scale  of,  Schultz 95 

Tin  feed-cases,  Gatling 595 

Tire 392 

Tool  for  first  boring  tube 177 

Tool  for  second  boring  tube 178 

Tool,  rifling !g3 

Tools,  cutting 164 

Tools,  machine 163 

Tools,  scraping ^4 

Tools,  shearing ^4 

Toothed  sector 400 

Tongs,  lazy 401 

Top  carriage  and  buffer,  8-inch 422 

Total  recoil,  curve  of 449 

Touch,  measuring 229 

Toughness  of  gun-steel 137 

Traces,  angle  of 402 

Traces,  attachment  of 403 

Traces,  direction  of 505 

Trajectory 347 

Trajectory,  division  of 505 

Trajectory,  flatness  of 538 

Trajectory,  form  of , 350 

Trajectory,  height  of 380 

Trajectory  in  air 356 

Trajectory,  maximum  height  of 380 

Trajectory,  rigidity  of 384 

Trajectory,  summit  of 366 

Transformation  of  general  equation  of  motion  of  projectile  in  bore. ...     48 


INDEX.  675 


PACK 

Translating-screw,  seacoast-guns  .....................................  264 

Tray-latch.  .........................................................  \  2^ 

Tray,  seacoast-guns  ................................................  263 

Traversing-gear,  12-inch  mortar  carriage  .............................  427 

Treatment  after  casting,  ingots  .....................................  j49 

Tresidder  process  ...........  ......................................  3I9 

Trial  shots,  range  by  ...............................................  4g4 

Tri-nitro-phenol  ..................................................  TIg 

True  mean  error  ....................................................  c™ 

True  value  of  f0  ..............................................  '  .....  2I3 

Tube,  bore  of  ......................................................  xgo 

Tube,  first  boring  ..............................  .....................  jyy 

Tube,  limiting  exterior  pressure  on  ..................................  211 

Tube,  second  boring  ................................................  ^g 

Tube,  turning  of  ....................................................  jgo 

Tube,  warping  of  ...................................................  !^y 

Tubular  magazine  ..............................................   gyif  574 

Turret-carriages  ....................................................  428 

Turrets,  Gruson  ....................................................  317 

Turning  angle  .....  .................................................  406 

Turning  and  boring  ...............  „  ................................  152 

Turning  tube  .......................................................  180 

25  per  cent  rectangle  ................................................  516 

12-inch  cast-iron  mortar,  steel  hooped  ...............................  259 

12-inch  mortar  carriage  .............................................  423 

12-inch  mortar,  breech  mechanism  of  ................................  268 

12-inch  steel  mortar  ................................................  258 

Twist,  direction  of  .........  .  ........................................  544 

Twist,  increasing  ...................................................  300 

Twist  in  terms  of  calibre  ............................................  300 

Twist,  uniform  .........................................  ...........  299 

U 

Uniform  riflin  g  .....................................................  299 

Uniform  twist   .....................................................  299 

U.  S.  percussion  fuzes  ............................................  334 

U.  S.  spherical  case  ................................................  288 

Use  of  Le  Boulenge  chronograph  ...  .................................  94 

Use  of  mercury  fulminate  ...........................................  119 

Use  of  Table  I  .......................  ...............................  511 

Use  of  Table  II,  probabilities  ....................  .  ..................  520 

Useful  practical  formulas  ...........................................  75 

V 

Value  of  A'.  ........................................................  57 

Value  of  A'o  ....................  ....................................  57 

Value  of  M.  ........................................................  65 


676  INDEX. 

PAGE 

Value  of  modulus  of  quickness 60 

Value  of  q 50 

Value  of  r,  calculation  of 65 

Value  of  r  for  maximum  velocity 59 

Values  of  A  and  B 54 

Values  of  a,  A,  and  fJ.  for  different  forms  of  grain 13 

Variation  of  elements  of  loading,  effect  of 69 

Variation  of  powder,  effect  of,  Noble  and  Abel's  experiments 24 

Velocimeter,  Sebert's 103 

Velocity  and  maximum  pressure,  variation  of 74 

Velocity  and  time  of  combustion,  variation  of 73 

Velocity  as  function  of  modulus 61 

Velocity,  change  of,  pressure  constant 70 

Velocity,  final 348 

Velocity,  initial 348 

Velocity,  initial,  by  experiment   83 

Velocity,  monomial  formula  for 63 

Velocity  of  emission  for  cocoa  powder 16 

Velocity  of  emission  for  flat  grain 16 

Velocity  of  emission  for  parallelopipedon  and  for  pierced  cylinder 15 

Velocity  of  emission  for  pierced  cylinder 16 

Velocity  of  emission,  spherical  grain 14 

Velocity  of  projectile 43 

Velocity  of  recoil 43 

Velocity,  remaining 348 

Velocity,  theoretical,  maximum 58 

Velocities  and  pressures,  smokeless  powders 130 

Vent-cover 247 

Vent-cover,  seacoast-guns 266 

Vernier  scale , 231 

Vessels,  shells  for  piercing  decks  of 282 

Volume  of  permanent  gases,  Noble  and  Abel's  experiments 25 

W 

Walls  of  guns,  thickness  of 217 

Warping  of  tubes 177 

Water,  effect  of  on  gun-cotton 112 

Water,  effect  of  on  mercury  fulminate 119 

Weight  and  specific  gravity  of  smokeless  powders 131 

Weight  of  bullet,  reduction  of 533 

Weight  of  cartridge,  decrease  of 539 

Weight  of  projectile 3IO 

Welding  of  gun-steel „ !4! 

Wetteren  powder I26 

Wheel,  object  of 3Q2 

Wheeled  carriages,  recoil  of 450 


INDEX.  677 

PAGE 

Wheels , 39o 

Whitworth's  hydraulic  forging 150 

Whitworth's  hydraulic  press 150 

Whitworth's  process,  fluid  compression 147 

Whitworth's  projectile 303 

Whole  range,  formula  for 365 

Width  of  grooves 542 

Wind,  effect  of  in  pointing 476 

Wire  guns 218 

Wires,  arrangement  of,  Le  Boulenge 87,  90 

Woodbridge  gun 219 

Work  in  terms  of  "  force  "  and  weight,  gunpowder 39 

Work  in  terms  of  length  of  travel,  gunpowder 40 

Work  of  gunpowder 36,  38,  39 

Work  of  gunpowder,  division  of 41 

Work  of  horse 401 

Working  of  Le  Bouleng6 88 

X 
jc  andj,  relation  between , 364 

Z 
Zone ,  probable 514 


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Church's  Mechanics  of  Engineering — Solids  and  Fluids Svo,  6  00 

"        Notes  and  Examples  in  Mechanics Svo,  2  00 

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7 


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"       Foundations 8vo,  500 

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8 


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9 


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10 


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Mosely's  Mechanical  Engineering.     (Mahan.) 8vo,  5  00 

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Sec.  I.     (Klein.)...  8vo,  500 

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Sec.II.     (Klein.) 8vo,  500 

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Steam  Engines.     (Du  Bois.) 8vo,  500. 

Lanza's  Applied  Mechanics 8vo,  7  50 

11 


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MacCord's  Kinematics 8vo,  5  00 

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"         Gold  and  Mercury 8vo,  750 

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12 


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Williams's  Lithology 8vo,  3  00 

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Goodyear's  Coal  Mines  of  the  Western  Coast 12mo,  2  50 

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13 


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2  parts,  12  00 

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14 


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15 


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16 


BOOKS 

ARMY  AND  NAVY  OFFICERS 

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JOHN  WILEY  &  SONS. 


ORDNANCE  AND  GUNNERY. 

For  the  use  of  the  Cadets  of  the  U.  S.  Military  Academy.  By 
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HANDBOOK  OF  PROBLEMS  IN  DIRECT  FIRE. 

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BALLISTIC  TABLES. 

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SUBMARINE  MINES  AND  TORPEDOES. 

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NOTES  ON  MILITARY  HYGIENE. 

For  Officers  of  the  Line.    A  Syllabus  of  Lectures  at  the  TJ.  S. 

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THE  SOLDIERS'  FIRST  AID  HANDBOOK. 

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ELEMENTS  OF  THE  ART  OF  WAR. 

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PRACTICAL  MARINE  SURVEYING. 

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AN  ABRIDGEMENT  OF  MILITARY  LAW. 

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A  MANUAL  FOR  COURTS-MARTIAL. 

Prepared  by  Lt.  Arthur  Murray,  1st  Artillery,  late  Acting 
Judge  Advocate-General,  U.  S.  A.  Third  edition.  18mo,  mo- 
rocco, flap,  ......  $1.50 

CAVALRY  OUT-POST  DUTIES. 

By  F.  De  Brack,  translated  from  the  French  (third  edition,  1863) 
by  Major  Camillo  C.  C.  Carr,  8th  Cavalry,  U.  S.  A.  18mo,  mo- 
rocco, flap,  .......  $2.00 

GUNNERY    FOR    NON-COMMISSIONED    OFFI- 
CERS. 

Compiled  by  Lt.  Adelbert  Cronkhite,  4th  Artillery,  with  Ballis- 
tic Tables,  by  Capt.  James  M.  Ingalls,  1st  Artillery,  18mo, 
morocco,  flap,  ......  $2.00 

ART  OF  SUBSISTING  ARMIES  IN  WAR. 

Capt.  H.  G.  Sharpe,  U.  S.  A. 
lorocco,     ........       $1.50 

THE  ARMY  OFFICER'S  EXAMINER. 

By  Lt.  Col.  W.  H.  Powell,  U.  S.  A.    12mo,  cloth,  .       $4.00 

ELEMENTARY  NAVAL  TACTICS. 

By  Commander  Wm.  Bainbridge-Hoff ,  U.  S.  N.    8vo,  cloth,  $1.50 

ATTACK  OF  FORTIFIED  PLACES. 

Including  Siege- Works,  Mining  and  Demolitions.  By  James 
Mercur,  U.  S.  M.  A.,  Professor  of  Civil  and  Military  Engineering. 

12mo,  cloth $2.00 

TEXT-BOOK  OF  ORDNANCE  AND  GUNNERY. 

For  the  use  of  the  Cadets  of  U.  S.  M.  A.  By  Capt.  Lawrence  L. 
Bruff,  U.  S.  A.  8vo,  cloth, $6.00 

HANDBOOK  FOR  LIGHT  ARTILLERY. 

By  A.  B.  Dyer,  First  Lieut.  Fourth  U.  S.  Artillery.  12mo, 
cloth $3.00 


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